It takes at least 10-15 minutes for my computer to get through the windows start up screen. Norton virus scans conducted on regular basis, but I do have teenage children in the house!

There might be lot of startup application scheduled to load when windows starts up. You could diable most of them via "msconfig" utility. Just type in "msconfig.exe" in run dialog via start menu. Go to startup tab, and scan the various entries there. Disable those you think are not important. This all results in bit fast startup. If you are not sure what entries you could disable or not, then let me know.

Next there can be malwares and spywares, do search for them and remove. All these also slow down system much. I'm giving name of two free spyware removers - "Spybot search and destroy" , "Lavasoft Ad-Aware". You could find them on www.download.com