To upgrade hardware nvidiageforce7100 to ...

i assume you have a pci-e slot on the computer. get atlest the geforce 8600 with 256. would cost you around 6000 bucks.

i need help of Ge Force 7300 GT vga card [256mb] of PC freedownload drivers

can you please inform me on your motherboard maker + serial number please?
Therefor i can determin if you have AGP or PCI/PCI-E compatable motherboard.

In accordance with the 2nd part of your questing on prices of your gfx card,
I recently bought 2 new gfx cards, Inno3d a well rated and factory tested card, both cards are factory overclocked to get peak performace from your investment whilst retaining a warranty.

In saying that most factory warranties are void as soon as you overclock your gfx card/s.

PCI-E
So the Inno3d 8800GT o/c 512mb, was pretty much the best bang for your buck @ $415au
AGP
As for AGP i had a friend upgrade his card to a XpertVision ATI X800 GTO 256mb, and he has not been able to stop boasting about the difference compared to his old card(somewhat similar to your 7100) and @ $125au
seems a bit of a steal since i paid well over $300 for a AGP (128mb) card less then 5years ago.