If your pc seems to be running slow after installing vista sp1, don't fret, this is normal. Prior to the update, vista's superfetch feature had built up a host of user specific optimizations that improve performance with the applications you use regularly.

During the sp1 installation process however, The superfetch data is cleared from the pc. To regain the performance optimizations, simply use the pc as you would normally. It should pick up a in a couple of hours or days.