codecx

I think that limitation is per-app though. If I don't run a page file, I've gotten my mem usage up to 5gb before, running a game like crysis, with steam, msn, outlook etc all open in the background.

But I digress. I did get it working , althought it was painful...and not perfected... But I'll explain it the short way and give you some extended info afterwards.

First, you need a copy of Server 2003, (Enterprise Edition if you want more than 4gb of RAM) You need a specific copy, that does not require a key on its initial install. If you use a version of server that required you to put in a key on the install, the change listed below, will not recognize the key and tell you to reinstall. Keep reading, you'll understand.
Once 2003 is installed, you need to setup a new user account and add it to the Administrators group. You also need to enable full hardware acceleration in dxdiag and in the Display Properties -> advanced -> Troubleshooting tab... Reboot.

Next, you a program called TweakNT 1.21. This is a funny little program that allows you to alter your windows configuration, giving you the ability to change a server OS to a client OS of the same type.

So, what you are going to do, is change your 2003 Enterprise Install and convert it to Windows XP Home. DO NOT DO XP PRO. PRO will almost always result in a BSOD. Its a waste of time.
When the PC reboots, it will be in XP home. Login with the user account that you created. In XP Home the Admin account is disabled by default.
Now you may install the latest video driver of choice. Reboot to have it go into effect, enable SLi and reboot once more for good measure.

After a few successful reboots, open up TweakNT again and switch back to Server Enterprise Edition.
Install the rest of your drivers.

Go online and download a program called nHancer, this will allow you to see if SLI is enabled or not. There are two things that will tell you if you've done it.

#1 it will say in big green letters "SLI Enabled"
#2 you will have tabs that pertain to SLi settings. Everything will be grayed out, but on a system that does not have SLi enabled, they are missing.

Ideally, thats all you need to do to get it working.

Now onto the problems you may encounter:

#1 Unless you own a legit copy of server 2003, chances are you are using a free 180 day trial edition from Microsoft, as thats the only copy that I know of, that does not require a ket on the initial install. So, you have to find a way to disable the timer. (Or ..at least I do... haha) My only work around right now is to image the PC on day 1 of 180 and ghost it whenever I run out of time. That will be my plan for the next 6 months at least.

#2 system instability. If anything goes wrong between reboots, you are creating a huge chance of failure once server is back up and running. I've explained the correct steps to take, but to get those, I ended up formatting about 17 times that weekend. I found that my ststem sometimes crashed, and that would cause problems anywhere from the windows installer service corrupting (So, can't install anything) to DirectX corruption., permanently disabling direct draw (no gaming for me!)

#3 Omega Drivers seemed to have more of a problem than the nvidia ones (Boo!!) Most of my formats were due to using it, as it was my ideal choice.

#4 its borderline piracy/hacking. Be warned. There will be blood on your hands after doing this.... can you live with yourself?

Thats about it.

The benefits of this are the stability of an XP OS and the optimized usage of Server 2003. I've been able to get Crysis running at 1280x1024, no AA, and all settings high, and get 55-70fps. It plays much smoother in DX9 than DX10. Older games seem to work OK, Fable, which is usually vey buggy, looks/plays beautifully.
GTA: SA doesn't seem to like my PC.. the textures are all gross. But all other titles seem to play great!

Good luck and have fun!