The suggestions below should fix you up.
Update and run your Anti-Virus program. Don't have one? You can run a free online scan from Trendmicro. When I have tested it it takes some time to run it but it may be time well spent if it can fix any problems.
Download and run http://housecall.trendmicro.com/
Download, update and run Spybot---http://www.safer-networking.org/ . Don't forget to use the Immunize feature.
Download, update and run Adaware---http://www.lavasoftusa.com/software/adaware/products/select_your_product.php
Since you just did a major upgrade? you may want to run disk cleanup and a disk defrag.
Start>all programs>accessories>system tools>Disk CleanUp
Follow the same path for a Disk Defrag.
I would also run a registry cleaner and a small program called CleanUp.
Download RegScrubXP--http://www.majorgeeks.com/download.php?det=2048
Safely cleans junk out of the Windows 2000/XP system registry. All changes made to the registry are fully restorable to it's original condition. You can make an exclusion list of registry entries that RegScrubXP will not display as problems. You can sift through a list of file extensions, company names, run upon startup programs, Internet Explorer history, and uninstall programs to delete what you think is junk.
Download CleanUp---http://www.stevengould.org/software/cleanup/
Free disk space, make your computer run better/faster and protect your privacy - all in one easy solution. All for free!