Vista worked just fine with X1 for me, after all, Vista is pretty much W7 with a bunch more services running by default.
If you have problems using X1/X2 on a Vista-machine I recommend tweaking-tips from tweakhound.com which made a big difference for me performancewise when using X1PE on a Core2Duo laptop.
As always when tweaking - think it through (does the tweak make sense to you?) & do 1 tweak @ a time.
The "Disable 8.3 names and Last Access"-tip is NOT recommended for a DAW though - if I remember correctly it causes plugin-problems.