ok my question is that I want to buy a new mobo that has PCIe 2.0 for my video card and the ram is ddr2 800 ive only got ddr2 667 sticks and I wouldn't have enough money to buy ddr2 800 ram if I got the mobo. the question is can i use ddr2 667 in the ddr2 800 slots on the mobo??? im looking at the asus p5n-d right now.....

that ram will work in that mobo. are you just getting a new one for pcie 2?

yes, and of course a better chipset, and I do plan to get ddr2 800 ram in the future but I cant afford it right now. so the ddr2 667's will work in the ddr2 800 slots just at 667 speeds, respectively.

pcie 2 is going to make no difference performancewise for you. decent mobo though.  

its got double bandwidth though.......

Todays gpus aren't powerful enough to utilize it. I have a 8800 gts g92 and it made no difference in pcie 2

well i still want the better chipset and the possibility to upgrade to ddr2 800 ram.

 
You could get that with an old P35 chipset motherboard.  In fact, you really can't do much better than the P35 when it comes to single card performance systems.  I've tested PCI-E 2.0 mode extensively and can say with absolute certainty that it has no benefit for current generation cards.
 
What about future generations?  I really doubt that you're going to be putting a new "GeForce 10800 Ultra" into your used system.  Next generation upper-mainstream cards will be no more powerful or bandwidth-demanding than current generation high-end cards.
 
Remember, it took around 2 years for AGP4x to show any real advantage.  It took around 2 years for AGP8x to show any noticeable advantage.  And it took around 2 years for PCI-Express 1.0 to show any real performance advantage over AGP8x.  You're looking at 2010 high-end cards?

 
DDR667 - DDR800 = no performance increase worth mentioning
PCIE1.x - PCIE2.x = no performance increase what so ever
 
better idea - upgrade to a motherboard with both DDR2 AND DDR3 for future support so you can jump to DDR3 and the memory will be ready for a nahlem system

 
Nah, plain DDR2 boards are usually more overclockable, perform slightly better, and are typically cheaper.  He can leave his DDR2-667 in the motherboard he already has until the entire system is outdate, and think about building a DDR3 system whenever that happens.
 
DDR2+DDR3 motherboards are kind of pointless.  DDR2 is still cheaper, so if he needs more RAM he can save big money by upgrading with DDR2.  By the time he's thinking DDR3 is needed, it will be cheaper.
 
You can't mix DDR2 and DDR3 on these boards, so upgrading from DDR2 to DDR3 means throwing away the old DDR2.

Keep your money and wait for a real upgrade.  667 to 800mhz is not noticable at all...

 
What is your current system specs atm anyhow?

And, what processor are you wanting to upgrade to?  Are you planning to use the same CPU?

This pc is basically going to be a meta-pc for me. so when I have money to get something better ill get it for this system and probably sell the old part on ebay or keep it for back up or spare. And yes I do know that I need a new processor but it was free as I pulled it out of a display at walmart while no one was looking (someone beat me to the ram).
 
Pentium D 930 @3.00Ghz
Asus p5n-sli nvidia 570i chipset
EVGA Geforce 9600 gt 512mb clocked @ 700mHz
Seagate 7200rpm 320gb hdd
asus dvd-rw
2x2gb gskill ram with a cas of 4
450 watt clear acrylic psu with 2 blue led fans in it
and a sunbeamtech clear acrylic case with a rear, front and side mounted 80mm blue led fans.

I hope you have a lock on your case, you know what they say.