Well, first, if you havent already I would get SP3 installed and any other windows updates that are available downloaded.
Secondly, go through msconfig and remove anything you dont vitally need to run windows. Having things running in the backround is the #1 reason a shutdown would take long. Also try a defrag and a thorugh scandisk from a boot disk.
\"Only two things are infinite, the universe and human stupidity, and I\'m not sure about the former.\"- Albert Einstein (1879-1955)