There are many reasons for a slow boot.
Try using our tutorial on this subject:
Slow Computer Checklisthttp://www.bleepingcomputer.com/forums/t/44690/slow-computer/
To manage your startup menu (programs that start when Windows does and run in the background), I suggest using Startup Inspector which is freeware you can get here:http://www.windowsstartup.com/
It is easier and less likely for the user to make mistakes using it because it does a better job of showing what ap the startup entry is connected to and therefore lessens the chance of stopping an ap that may be important to keep in the startup menu. (like an av program or firewall, etc)
After doing as the checklist advises you should take advantage of the Windows One Care Free Scan
Go to Windows Live Onecare Free Scan (using Windows Explorer only)
It will say "Get a free PC safety scan"http://safety.live.com/site/en-us/default.htm
Make sure you click "Full Service Scan"
in the middle of the page and not the "Try It Now Free" on the right side.
Allow it to download the Active X components.
Choose "Complete Scan" in the window that opens
Do not click on anything else that offers you a free trial or to sign up if you live in the US.
Allow it to scan - it may take quite, maybe two hours or so depending on how big your hard drive is and how fragmented your registry and drive are.