Nope, I'm running on a Dell that came with a X300SE(Suckyest Edition) and is now on a X1600 XT, I don't see why Dells would be 'impossible' to upgrade, they might be harder because of strange sizes on some parts, not sure if thats true though. You might want to go with a Dell XPS 400 with the E6600 Processer, 2 gigs of DDR2 Ram, 320 GB harddrive and the lowest video card and then get a ATi 1900 XT (258 mb version). With one year insurence it totals to (Including the 1900 XT) $1700.
it might not be the best idea to get a Dx10 card yet because they have MASSIVE power requriments and a 1900 Xt will last you 2 years at least.
I'm using US$