I start by removing spyware and/or viruses. Two really nice spyware tools are SpyBot Search and Destroy and AdAware. They are both free tools and can get 99% of the spyware out there. Secondly if no antivirus is installed, I like to use AVG available at http://www.Grisoft.com .
Cleaning up the Temp folders on the hard drive is next. Depending on the Operating System, there will be a few of them. In windows 98/ME/XP delete all the contents of the c:\windows\temp folder and in 2000 c:\winnt\temp. Also in 2000/XP you will need to clean out the users temp folder. It is located in c:\documents and settings\username\local settings\temp. The local settings folder may not be visible but you can make it viewable by going to Tools/Folder Options/View and select Show Hidden Files and Folders.
Next you will need to clean out all the temporary internet files. You can right click on the IE ocon on the desktop and select properties and delete all internet files there.
Lastly, I like to clean up the registry. Go to Start menu, then Run and type regedit and click on ok. This will bring up the registry editor. The 2 major places to clean are some of the startup items. The keys to remove/review are located in HKEY_CURRENT_USER/Software/Microsoft/Windows/Current Version/Run and HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/Current Version/Run there are a few other runs in there that you can review and remove subkeys if you like. Be careful what you remove, you won't keep your computer from booting, but you can delete startup items.
I hope this is of some help, as it keeps my network and all my friends machines running smoothly. I can stress the importance of antivirus and spyware tools. They will keep you clean for the most part.
Blayne Beham
Network Admin
Inter-Americas Insurance