How did you effect that change? If you simply changed the extensions, that won't do the job, as the content will still be in the old format. You need to let Word open the files (with their former extensions), then use File|Save As.

Given that you're using Office XP, the native format is:
Word 97-2003 (*.doc)
You could also save as:
Word Document (*docx)
or, if the files have macros:
Word macro-Enabled (*docm)
These latter two formats are native to Word 2007 & later.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]