Winword.exe is the file that runs WORD. In XP, it is in the folder: C:\Program Files\Microsoft Office\OFFICE11
My guess it it shares spell check with other programs, like FrontPage, through some dll. That dll might have been replaced by some malicious virus. I usually check the program folder for any new programs or dll's that were recently added that I didn't add. That can be a clue. Use the Search feature and type in *.* or *.exe and *.dll to check all files and limit the search to when you think the problem first happened.
http://Computerhope.com (Great place to ask these types of questions.)
Also
http://BleepingComputer.com
http://forums.techguy.org (Good but closed today.)
Sorry, but I don't know the dll name that I am assuming is used to spell check WORD docs. The good news is that if you can find it, you can easily replace it. The bad news is that if a virus caused it, you will want to find and remove that, too.
Pete