If you have ~$190 to spend, get a 6800, period. Even though it has less memory, it'll be much faster, and speed is what you're after. You won't care how pretty the 9800P looks if it's too slow to let you play without getting killed. Plus, a 6800 actually uses *less* power than a 9800P, which should increase the chances of it working in your PC.
If $190 is too much for you, then get a ~$150 6600GT (
this one: comes with two good games, the same outputs, and should have a slightly better/quieter cooler than the eVGA). I'm with Rollo: even though a 9800P is as little as $120 new, it's still slower (much more so in Doom 3). The Leadtek I linked to also comes with two well-reviewed games and an HDTV (component out) cable, which makes it at least as good a value as the 9800P, IMO.
So, I think your two best choices are a ~$150 6600GT and a ~$185 6800 (and, specifically, those Leadteks). The 6800 will be slightly faster (and has the possiblity to unlock four extra pipelines, which will make it much faster) and draws less power. The 6600GT has HDTV output, probably better WMV9HD acceleration, and is available now. Your call.
But tell us your power supply specs first! Yuo're going to have to open your case to install the video card, so get some practice now and open it to read the line amps for us. If you don't see any info on the PSU by just taking the side off, then detach it according to page 49 of the
instruction manual. If you can't see a total wattage figure, at least tell us the number for the +12V line. Take the five minutes now to find out rather than risking breaking your machine or having to return the card.