I have a Dell 2400, I run Mandrake 10.1 on it with absolutely no pb so far. I've also tried other live CDs and they have all worked
fine : no pb with the graphics card, except the Debian-based ones like Mepis and Ubuntu. So I advise you to avoid them
on this computer.
Maybe they want you to buy a more expensive box ? Wouldn't come as a surprise, would it ?