Wait, do you have a PCI-Express slot? As far as I know, they dont make an AGP 7300GS.
You'll have to find a decent AGP card unless you are going to buy a new motherboard.
There arent many options for AGP, and since they usually cost more, you can probably get a decent PCI-E motherboard and a good PCI-E card for just a little more than a decent AGP card. If you just want to stick with AGP though, either of these would fit your system pretty well:
6600GT for $132
6800GS for $225