|The graphics chip is built into the motherboard. You can't remove it, you have to disable it & change the initial display setting in the BIOS to the PCI slot.|
Still, I strongly disagree with what you're doing. Your system is not meant for Win7, or if you prefer, Win7 is not meant for your system. It does NOT meet the minimum requirements. And assuming you already know that, what is it that you're trying to prove? That you can take a system that runs XP acceptably & make it Win7 poorly?? Bravo!
I have no doubt you're going to do it anyway so I suggest you cut your losses. Do NOT buy a new PCI card. Try some local PC shops in your area to see if they have any used cards laying around. Try the local flea market (if you have one). Go to Goodwill, Amvets or try FreeCycle. As a last resort, try eBay. You should be able to find a standard PCI card for $5-10. If you spend more than that, you will have spent too much.
EDIT: You don't even know what a PCI slot is?? Yikes! Here's your motherboard: