Gosh that is strange, I've had X1, Xtreme2,3,4 and 5 running on Windows 7 RC since it was available and now I run Xtreme Pro on Windows 7 Pro 64 bit on a networked machine without the dramas you're having.

What do you think?
I think you might start looking for a common denominator outside of Xara Xtreme 5 which could be responsible for causing the poor performance you are having.