Well, if your 8500GT is a integrated card it will be solderd to your motherboard and doesn't use a slot. If it does use a slot you can take it out and put the 450 in.
The 450 is dx11 but it's not a very good gaming card actually, don't expect to much from it. If you wanne have a good gaming card at least go for a 460, but only if you have a good processor, i saw there is a wide variaty of possible cpu's from pentium D till quad core. Which one do you have ?
sorry i didnt reply i though email notiffies me if someone helped me sorry again i have core 2 duo e4500 2.4ghz and cant buy from newegg casue i live in lebanon how about u advise me for the best card on this website http://pcandparts.com/price.htm
I think a 460 would be to much for the processor. ( not complete sure though )
For a 450, this is a nice one ; Asus Geforce GTS450 1GB DDR3 Dual w/TV
For a 460 this one ; Inno3D Geforce GTX 460 1GB DDR5 Dual w/TV $219.00
im planing to go for a new system next year for now im going with the gts450 casue its cjeaper or i may going hd5770 next your i think i go for gtx580 sli wehn i get new bored and processer and moniter