Well then, there is a question why upgrading to the new OS. i dont know much about it, but as i know with the direct X 10 available only for Vista, MS will eventually force us to do so, but i think an older OS like XP should be fine for some years.... until then they may fix all compatibility issues, >if any<.. i remember back when XP came out, lots of games were not working on it, but after some time they fixed the majority.
As i said, i would not bother upgrading to Vista at the moment it comes out, as i learned to be a bit sceptical about MS's "improvements"
edit: Also, as DW is relatively new ga.. software
i think it will run on Vista anyway