take a pic of the side sticker on the psu, it lists all the amp specs. (i think its ironic its called "zero power"). as for best video card, for any dx9 game try finding a 9800gt used somewhere, or new... some stores in the usa still sell them new. or, if you plan on upgrading to win7 (or find a nifty DX11 hack for xp, if it exists) then go with a 6770/5770/6850/5850 or gtx460/gts450/gtx550ti/gtx560 non ti.
also, a cheap cpu upgrade would be to get an aftermarket cooler and overclock that E7200 to a 1333fsb (333 bus speed), should bring you to 3.16ghz from 2.53ghz. some AS5 and a $30usd ish cooler would do. most "tower" style coolers with a 92mm fan should be ok. had a similar one on a pent D 820. overclocked from 2.8ghz to 3.5ghz and it ran cooler than it did at stock speed with the stock fan.
also a note, if you decide to upgrade to 4gb ram (i'm assuming ur running 2x 1gb) winxp won't be able to fully use all 4gb. if you went with 2x2gb you'd get dual channel and have 4gb for when you upgrade to win7. or, you can keep 1 1gb stick and replace the other with a 2gb (if you do this make sure the timings for the 2gb stick match the 1gb stick and same speed). this option will be cheaper, but you wont be in dual channel mode, however I haven't seen that big of a performance hit with this option, at least not with pc's of your specs. I'm sure higher end stuff would see a difference.
I think you could do all of the above for around 200ish. $40 for the cooler, $40-45 for a single 2gb stick, and a used gpu at the performance level of a 9800GT for around $100-$125. should get you by until you get a new rig. heck a 9600GT did just fine for me with the rest of my pc spec (see over to the left) and i played starcraft 2, crysis, borderlands, modern warfare 2, etc on high-very high settings. most at 1280x1024. at 4xAA/AF, crysis w/o AA/AF (btw if you want to just get by with a lower spec card, a GT430 is on par with 9600gt performance and should handle any dx9 game fine as well, and will run on as low as 300w psu. if you get one get one with 128bit memory. can be had for less than $75usd. it'll run circles around that 8500gt you had, which had 16shaders, 8rops. the GT430 has 96shaders, 16rops., actually looks like its 3,300 in ur price list for the GT430)