ya don't get the 8600GT sir.
after looking in you system specs. you already have the 8400GT.. that is almost just as good as the 8600Gt. you will notice very very small increases in performance.. if at all. don't get that.
spend the extra 30 or so dollars.. that in the end are WELL worth it. and get the 8800GT from newegg.com. they have one for $110 now. and the 8800GT is easily about Double the performance of the 8600GT
the 8600GT are around $70 or so everywhere I look new. and then you have
8800GT.. double the performance of the 8600GT. and it's only $110.
Newegg.com - PNY VCG88512GXEB-FLB GeForce 8800 GT 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Desktop Graphics / Video Cards
PNY is not the best brand ever. but they are almost all the same card. with a different sticker. so might as well get that. otherwise get the eVGA, or the XFX