I used to have a TNT2 a while back. Served me well : )
You have an AGP video card, it's an older standard of slot for GPU's that is unfortunately outdated. Most computers in recent years have adopted the PCI-Express slot standard, and it's been updated from PCI-E 1.0 to 2.0 to 2.1.
If you're set on replacing your TNT2 and you don't want to buy a new computer, then any 8x/4x AGP video card should do, provided you have the necessary power supply for it.