that motherboard will fit in just about any case accept maybe a SFF.
It supports dual channel and SLI.
Best thing to do is buy the motherboard and get a dual core opteron.
they are about the same price as the X2 cpu's and they tend to clock up a lot better if yer into that kinda thing.
Also, all opterons have 1Mb per core, unlike the x2, where several have only 512KB per core.
And yer videocard will last you long enough to wait for the directX 10 cards, but if yer in dire need of a graphics upgrade, I'd just get one right now, it's not like directX 9 cards will be worthless when dx10 cards come out.