Is there any problem ?
hardware problem for playing games ?

 If you are asking is it really as easy and straight forward as it sounds then the straight answer is no it isnt.
The games have to support SLI, I dont use it but would think most newer titles would do, maybe someone else can coment on that. You can some times have to wait fo rthe drivers to support the newer games and also it dosent mean you will get twice the FPS, (Just in case you was of the impression you did).
 
 Why dont you elaborate a bit more on what it is you want to do and we can help more. You mention hardware,Well some motherboards support Crossfire some support SLI, so really we need to know more before we can advise you properly.
   Mactronix

Thanks Mactronix buddy
i want to get more power! on games
so, i want to know which graphic card should i use ?
whats the most powerful VGA ? is it better to wait for 9800 series from NVidia or use 2 x 8800 ?  
whats the best 8800? GTS ? GTX ? GT ?

 Well general rule of thumb is to get the best single GPU you can afford. If you are in no hurry then it may pay you to wait and see what the 9800 series has to offer, I have seen a couple of alleged previews and they sound good but we wont know for sure untill it comes out. These things have been way off in the past.
Do you have a system you are upgrading ? If so what size/res monitor will you be using, How about the power supply is it up to running a big card ? There really are a lot af variables and as i said i can only give general advice without knowing more.
 At the very least i would wait for the new ATI cards the R700/770 and see what they have to offer. If you are set on Nvidia then waiting for the 9800's could result in price cuts for your current best bet which is a 8800GT or GTS. But make sure its the G92 versions and not the old G80 ones. The G92 cards have 512 MB while the older cards with the same name(Thanks Nvidia)have 320/640. If you are itching for one now and are not running a huge monitor say above 24" then this card is a good price and close to the fastest thing going at the min.
http://www.newegg.com/Product/Prod [...] 6814127329
   Mactronix

Almost all games support SLI if they don't then it ain't worth playing them as they are so old or so bad nvidia haven't even bothered doing drivers.
 
 
IMO SLI is great. As long as you arent CPU bottlenecked which is one of the reasons why it does so bad at lower resolutions compared to higher ones.

I have two BFG 8800GT in SLi and the only problem is heat/noise of stock cooler.  I have a quiet case and typically don't game with headphones, unless when I need a mic.  So I replaced the stock coolers with aftermarket ones.   performance wise, they are great.  In Crysis, they easily outperform any single card out there, which makes a playable difference.  In other games it depends on your settings.  You may find 55 fps for one card and 80 fps for two cards.  Nice gains, but isn't 55 fps playable enough?  Oblivion I see massive gains out in the foliage (most gpu intensive areas) but not in towns around NPC's (most cpu intensive area).  Overall it's very impressive to see it laugh at the demanding foliage that took last gen cards down hard.  
 
I haven't ran into a game issue yet because of SLI, but granted I have only played maybe 10 games.  If you look at games that the NV drivers default to single card instead of SLI, there isn't much there you would care about or need more performance anyway.  Big titles like (like crysis) will have support at launch or very shortly after.  Not so polular titles you may find never get support .  Worst case, you have to make a game profile that disabables SLI when you fire up that game.
 
Anyway, go for it.  You may have to play at high res or use fsaa to get any benefit. But I'm thrilled to have gone with two 8800GT instead of one 8800GTX for the same cost.  

As of the 169.28 drivers here are the games that the drivers default game profiles default to using one card instead of SLI: (can't say a single game there bothered me to see)
 
Games with Single GPU SLI Specific Profile:
Sims 2 – all versions
Hitman Contracts
Thief 3
Clear Sailing
Fire Truck
City of Hero’s
FIFA Soccer - All Versions
NASCAR SimRacing
Grand Theft Auto: San Andreas
Boiling point – Road to Hell
Dungeon Lords
Tiger Woods – all versions
NHL – all versions
Neuro
Heroes of might & magic 5
Blitzkrieg II
Draken: Order of the Flame
Cossacks II
Heroes of the Annihilated Empires
Medievil : Total War
Arx Fatalis
Juiced
Priston Tale
Maelstrom
Instinct
Myth War
Voyage Century Online
HuangE Online
Infernal
Dragon Throne & Expansion
Chinese Paladin 4
 
 
In contrast, check out the list of SLI optimized games here:
http://www.slizone.com/object/slizone2_game.html
 
 
There must be 500 games listed there, although some are on both lists.

to Mactronix
 
Pal, GPU mean is VGA ?
when can i get 9800 ? i mean the release date
at last what do you prefer ? 2 x 8800 or 9800  
Monitor res is 1680x1050 is there any better monitor with larger res ? i want to know about it
what Power you prefer for 2 x 8800 ? do you know release date of R700 of AMD ?
how can i check it G92 ? so gonna get 8800GT 512 MB  
 
to Hatman
 
Buddy, i dont mean to support  
i have another question : if i got 2 x 8800 and i install CPU-Z software to show me my system is it show us 1024 mb or just show one graphic card ( one 8800 ) ?
 
to Pauldh
 
Dear Paul, so the main problem is heat so what power and cooling system should use ?
80 Fps is great! so you can play Crysis easily with 2 x 8800
thanks for list

Crysis is not the best coded game around at the moment IMHO, however with a pair of non OC'd 8800GT's all settings on high except shaders which I leave on medium and no AA, resolution @ 1680 x 1050 gives 29fps or so outdoors and 70+ fps indoors.

 
Whoa, the 80 fps comment was just an example for other games like, like COD4.  example: http://www.firingsquad.com/hardwar [...] /page8.asp
 
Crysis I see huge gains with SLI, but never see 80 fps. Shoot if you stay above 25 fps, crysis is pretty smooth.  
 
As far as heat, it depends on your case airflow and room temps.  If you have great air flow, cool ambient temps, and don't mind some fan noise the stock coolers are OK.   I have a quiet system (Antec Sonata II case), and my two 8800GT's with aftermarket cooling (Zalman VF-900 CU dialed down in rpm with the included fanmates) don't go above 62 degrees (c) now.  But with the stock coolers, I saw the top card hit 93 degrees and the bottom card 88 degrees.  I didn't like that so I controlled the fans myself (riva tuner or drivers) to keep temps down.  But two of those fans are obnoxious above 70% fan speed.  That kinda ruled out overclocking fo me, and I worried come warm summer months I'd need to push the fans higher (say 89%), which is unbareable (IMO anyway) if you don't game with headphones.  
 
Another note, my Q6600 at 3.0GHz now is 8+ degrees cooler than it was before when I used the stock 8800GT coolers.  This totally blew me away, and was an unexpected pleasent surprise.  But I hit 63 degrees highest temp on a core in core temp before in crysis,  now no core has gone over 55 degrees in hours of crysis with the only change being my GPU coolers and possible 1-2 degree (F) room temp fluctuation.  Shoot, now I can push the Q6600 beyond 3.0GHz as I didn't bother trying before because of the core temps under load.  (stock intel fan just).  
 
Anyway, if you care, here they are after installing the VF-900 on one card:

Thank you all
now whats the best VGA available ?  
2 x 8800GT 512MB or 1 x 9800XT ? or another ?
Thanks

Hey Guys, I just bought 2x8800 GT.  
I have 27fps on the GPU test with all settings at high. and to my surprise I drop to 17 when I enable SLI :-/. That hurts!!!
Im running the 1.1 version and the nvidia drivers just before the June 08 release

What in the name of god are you talking about? lol "the gpu test"
 
Make a new thread, include more information - you just tacked this onto the end of a 4month old thread.

lol. thanks google.... didn't check the date. Ill do