I did it so far on my desktop and this is how I did it
Installing Vista Service Pack 2
check to see if you have kb955430 (you must have this before you install the
sp)
before doing the upgrade
Use Ccleaner
Do a virus scan to make sure you are clean
Do your antispyware scans to make sure you are clean
Defrag the computer
Do the upgrade using the full package instead of WU
Once done- test everything especially sound and internet
Do another defrag
When doing it this way I had no problems
I have not done it on my laptop yet- I am going to wait awhile because I
need this for my seminars and one is next week and I do not want to find
problems
It seems more people are having problems on the laptops installing the sp2
then desktops
robin