Make sure WordPad is the default for opening *.DOC and *.RTF. Open
My Computer, Tools, Folder Options, File Types. Scroll on down to
*.DOC and *.RTF in turn. Make sure WordPad is shown in the
application to open option. If it isn't, change it to WordPad.
I had the same problem after installing SP2, the only way I could open word 6.0 files was with MS Works, Word Processor and then file them with Rich Text Word.