Can my computer run this graphics card?

My computer is old and junky, and I cannot afford to replace it any time soon, so I was going to upgrade it (1 more gig of ram, Windows 7, new video card). I want to make sure it's going to work before I spent money on it.
Video Card: http://www.bestbuy.com/site/BFG+-+NVIDIA+GeForce+8400+GS+512MB+DDR2+PCI+Express+Graphics+Card/8990407.p?id=1218007083381&skuId=8990407

300 Watt PSU
NAGAMI2L Motherboard model (http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00683218&tmp_track_link=ot_recdoc/c00716361/en_us/c00683218/loc:1&lc=en&dlc=en&cc=us) so you guys know what my motherboard has as far as slots and stuff
Compaq desktop
NVIDIA GeForce 6150 LE integrated graphics
2.4 gb of RAM
Windows XP (Planning on buying windows 7 this holiday season)
2.2 ghz single core AMD Athlon 64 3500+

I have had this computer for just over 3 years.
Thanks!

The video card might not work with Windows 7. I personally hate Compaq computers, they've very... un-customizable. Lots of proprietary stuff involved. Good luck.