You may also search http://search.microsoft.com/search.aspx?mkt=en-US&setlang=en-US for Microsoft help
I don't know about THIS problem, but I have read in the past that Microsoft has an updated installer that you may download... search at the above link
You don't say which antivirus program you're working, but Norton is notorious for screwing up systems.
Beyond that, make sure you've got a good 50 gigabytes of free, clean, defragmented space on your C drive. And, since your computer is likely to be at least 3-5 years old, you may want to run a program like (my personal favorite) Advanced System Care to ensure all is cleaned and tuned on your system.