Hmm. This is a common problem sometimes when the computer has a lot to load up. Even when windows has loaded and the desktop is up, it is still loading some of the programs, like norton, msn, etc.
There is one way of finding out whats slowing the boot up, but I don't know exactly how to use it I'm afraid.
Its made by Microsoft and is called Bootvis. It is designed to tell you what is taking its time.
Maybe someone can help you with that, but a search on Google should find it.
Other than that, its not really a problem, but by any chance have you tried a Defragmentation from Start, Programs, Accessories, System Tools, Defrag?
That will clean up your hard drive, placing everything it needs at the start of the hard drive to load up faster. Its best to do that in Safe mode when you can, by pressing F8 I think it is, at bootup, and selecting it.
Plus, have you tried running Disk Cleanup, from the same location?
It'll then display a list of things found it can delete.
Make SURE YOU UNCHECK the option to delete Compressed Files (usually starts to happen after 50 days of a program not being accessed on the hard drive)
and then run it, deleting everything the computer doesn't use anymore.
I hope this helps