Help with OEM case airflow

You've got a tough job here. As is the case with most OEMs, the boxes are relatively low volume with few intake/exhaust fans. The 80mm exhaust fan at the rear of the case is a real problem...a 120mm would have been much better. Don't count on getting appreciable cooling from the PSU...its fan is designed to cool the PSU, not the case; the volumetric exhaust flow is minimal. So what options to you have?
1. Use a video card that exhausts air outside the case, e.g. eVga Akimbo - you can actually buy the Akimbo kit from eVga for non-exhausting cards.
2. Install a rear exhausting slot fan just under the video card. These fans are usually cheaply made, don't last long, and require frequent cleaning. Try to find one with a ball bearing fan; stay away from sleeve bearing fans.
3. Replace the 80mm stock rear fan with a higher volume solution to exhaust more case air - will be noisier though.
4. Install an auxillary 80mm in the front, if intake holes are present - this will reqiure you to drill holes in the front to mount the fan, or use "cut to size" velcro strips to hold fan in place (jury rig solution).
5. Install external water cooling kit (could be a laborious solution, considering the limitations of your case).
6. Have a machine shop cut a 120mm fan mount opening on the side panel (you could do this yourself using a metal cutting blade on a reciprocating saw or better yet, a band saw if you have one...after drilling a pilot hole). I recommend using a machine shop however, since their end result will look better. Some shops can use a hydraulic press to neatly cut the hole.

Solutions 1 & 2, would be the easiest.

Good luck!

Quicker reply then I anticipated. Thanks for the input. I was trying to look for a good positive pressure solution, which is really tough.

As to your options, I've been thinking about a PCI slot cooler, those are cheap enough. I can also ghetto rig an 80mm fan in the front, there are intake holes (though covered in front by a plastic cover)

The Akimbo cooler is $40 bucks, which isn't too bad, but for that I'd rather get a $50-60 dollar case with much better potential. Water cooling and machine shop is also much too expensive.

Nevertheless, thanks!

Actually, you want a slight negative pressure in the case to avoid hot spots, although not so negative that the PSU fan is unable to pull air through the PSU.
Would it be possible to cut a hole in the top of the case? Heat rises, so of course that would be an exhaust.
You might also cut a few vent holes in the bottom of the case. Make a frame out of craft sticks with a piece of screen or pantyhose stretched over it as a dust filter.

I've reversed the airflow once, which did work out okay. Problem I really had was ducting the PSU heat away from the rear exhaust which was to be the intake.  

But since you have a 8800 that doesn't vent heat out, that would be the other problem with making the rear exhaust an intake.

The only idea I could mention, which would mod the case some, is to make a hole on the bottom of the case, which some kind of shrowd to point it at an agle, say 45 degrees. So it's pulling air from the bottom of the case to push it twards the middle of the MB for the CPU.

If you go with that type of idea, perhaps getting a dust filter for that, depending on how dusty the floor maybe, and if there's not enough clearance, using different footings on the bottom to raise it up.

Also, you'd have to gut the system to drill the hole for the fan on the bottom.

Excellent point. You definitely want to do this to avoid any chance of getting metal filings on your mobo or other circuit boards in your system.

Since there are not any intake fans and only room to mount one 80mm in the front, you will never get positive pressure with this case. But that's fine. And you certainly don't want to reverse the psu fan and blow hot air into the case. Just mount the front 80mm intake however you can, screws, zip ties, etc, and mount the rear 90mm fan in the spot provided. The negative pressure will suck cool air in from the side grill and the front of the case. That's the best you can do. You could also cover the side grill with a fine mesh silk like cloth material to keep out dust. I've done this before. Held it on with tape and it worked well.

ejay had a good analysis on this one.

Your cheapest solution is to just remove the side panel and direct a small house fan at the innards. You probably would not even need filters then.

Seriously, though, I think I would spend $60 shipped on an Antec 300 case.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

You get a case with superb cooling, filters and fans are included.
By the time you pay for extra fans and coolers, the cost difference will be small.

Do you have any vents on the side of the case, if so zalman makes a bracket mounted fan. Comes with bracket and 90mm fan, I think its 90mm but works really nice when mounted to screw holes where the pci slots are if you got a case with vents there.

Fry's has that bracket fan zalman FB123 is model number. It can also be used to cool the north brdige chip as well depends how high or low you mount it. I use mine low to pull cool air in from the side to cool my 8800GT, also make sure to use software Ntune or other utility to turn up GPU fan speed when playing games.

Your best bet is to do as previously suggested, get a case like the Antec 300 instead of trying to jury rig something with the poorly designed Gateway case. To make your current case work properly would require extensive investment of time plus some cash, plus you would have to research proper cooling theory. While the last is something you should do in any event, the time and effort in fixing what you have is not worth it.

Agreed.. much easier to buy the case that has good airflow, then trying to mod it.

Unless you enjoy modding, then buying the case with good airflow would take some of the fun out of it.

But then if it's a main brand (Gateway) you'd void the warranty, and perhaps the OP would not be the type to even take a saw to the case.