I believe you may have been misinformed about the upgradeability of the Inspiron 7500's video card. AFAIK there's no good reason why it couldn't be done, but I don't believe there's a supported upgrade path. Its little ATI graphics subsystem card is tailor-made for the computer. Even if you can get a replacement GeForce or other video card with the same form factor you'd still have the issue of whether or not the new graphics subsystem would be recognized and used properly by the BIOS. The last BIOS revision released for that notebook is A14 (Dell's version number), and that was created quite some time before any of the GeForce portable cards I know of were designed.
Don't get me wrong. I'd be delighted to learn that I was wrong about this. I own an I7500 and support about a dozen others whose users would all love to experience a display with a bit more panache.
Have you tried looking at the DellTalk forum? It's not much of a forum because the interface is one of the dumbest I've ever seen, and its various functions (like search and even link color changing) are almost always broken, but there are a few people there who have hammered this topic to death without any resolution that I've ever seen reported. Maybe you can find someone who can help in that forum.
- Collin