I am not clear from your post what the problem is you are having. Your profile says that your computer knowledge is advanced, and so I expect that you are fully profficient with using Windows Explorer, and the Control Panel applet Add/Remove Programs.
If that is the case, then why would you suppose that "junk" is lying deep in your Documents and Settings folders? You will know that, unless you specify otherwise when installing a program, it will install under it's own sub-folder in the default location of the Program Files folder .
I expect you have already used Windows Explorer to examine your hard drive contents, and have used the Add/Remove Programs applet to remove any unwanted programs you have. I also expect you know that using Add/Remove, or using a programs own Uninstall program doesn't always remove the entire contents of a program. Some junk may remain in the progam's folders that you will need to delete manually using Windows Explorer.
Can you please explain more about Office and Norton Systemworks? You say that each time you start any Office application, (I take that to mean Microsoft Word, or Excel, or Access, or PowerPoint, or FrontPage), Norton Systemworks makes you cancel an installation update. What installation update? How does Nortons SW make you cancel the update? What is the connection between opening an Office application and Nortons SW cancelling an installation update? What error messages do you get?
You say that now attempting to install PC Anywhere fails completely because of an old ATI driver setup program running instead. How do you know? What error messages do you get to link the two?
What junk files are you looking for? Norton Systemworks? ATI driver setup programs?
You mention the newest version of Windows. What newest version? Windows XP? If so that has been out for some years now. Or do you mean the upgrade to SP2?
You have said you do not want anything vague like, "look for temp files and delete them", so the information below is probably duplicating what you have already done.
Goto Start > Search, and search your local disk for tmp files and folders. Make sure you search for hidden files and folders as well.
Then when that search is complete, goto Start > Search again, and open up a new search window, to look for temp files and folders.
In these two windows you will have listed all files and folders with tmp or temp in their name, and you can then consider each one individually.
You ask if there is any single or simple answer. As I am not sure what the underlying problem is, I can't say, but I suspect there is no simple or single answer.