Comment from the sidelines:

Switching to Vista is not an upgrade. It can most kindly be described as a change of platform. (Other people have far stronger words .)

Unless there are specific features you need in Vista, you might be better advised to wait for Windows 7 sometime later this year. It apparently fixes many of the problems and annoyances of Vista, including network setup.

However, you will not be able to upgrade from XP to Windows 7: you will have to go through Vista first.