In all honesty, I would really suggest you dish out $50-100 and buy yourself a new case. I know you just bought that one and it may seem like a waste, but I've heard that Dell cases are the worst possible cases for everything.
Of course a bit mod modifying and some work can turn any case into what you want and need it be.
Also, the x850 is a PCIe card, so you're going to have to make sure your board has an open PCIe slot for such a card, rather than an AGP slot.
If you have any other questions, feel free to inquire, and I will answer to the best of my ability.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w