JORDAN --
You could save yourself a lot of money and just get the best video card on the market. Your computer has the same specs as mine (Dell Dimension XPS T600r ??). You might could use some more ram, but 256 is more than enough for gaming. A nice sound card could do wonders too. Something like a Creative SoundBlaster Live, or Turtle Beach card would be great.
I get my rough pricing from PCNATION.com
GeForce3 (origonal release) $300
256mb PC133 Kingston X2 $70
SoundBlaster Live 5.1 DD $70
$440 for a pretty conciderable boost in 'gaming' performance, depending on what you already have. What I'm getting at is ... don't waste money on stuff you don't need. You don't need a new case, motherboard, processor, hard drive, DVD/CD-RW or monitor (you've got the P991 flat CRT, eh? Me too, it ROCKS). Just buy what you need. But if you have problems, Dell is going to want you to first put the origonal stuff back in the computer, to rule out someone else's hardware being the problem. No biggie, just keep it in mind.
As far as the OS goes, Windows 98 still has the best support and performance for gaming. Windows 2000 works, but I get pretty lousy framerate in some games, due to bad OpenGL support, and weak Direct3D support. Unfortunately Win98 isn't an option anymore, but as nearly as I can tell, WinME does a fair job. I just don't like all the WinME crap that comes with it, yuck!
Oh, I guess I should mention that I'm a System Administrator for a large advertising agency. We use all Dells and Apples. I also do the same for the marketing departement of my university, but the pay isn't quite the same (: At the advertising agency I pretty much call all the shots, that pertain to computers. My slogan, "If it's more complicated than a toaster, and it plugs into the wall, it's my business."
~LoudMusic