To find out about your VGA card you can list your pci hardware with the command 'lspci'. But you already know you have a GeForce 7600 so there is no need to find that.
Most probably slackware didn't detect your hardware correctly because you need to get the driver from nvidia.com. Follow their instructions to install and it should configure xwindows for you automatically.
If you still need help with specific things, just ask here and I'm sure someone will know the answer