OpenOffice/MS Office SharePoint problem?

When I try to open any Word 2003 document in SharePoint (i.e., open the doc in order to edit it), I keep getting error messages. Naturally I didn’t capture the exact error text, but it led me to suspect that the problem may be occurring because OpenOffice, rather than Word 2003, is trying to open the document. I double-checked that the “doc” file extension is associated with Word, not with OpenOffice. However, there are literally dozens of unfamiliar file extensions that ARE associated with OpenOffice, and I don’t have time to change them all.

Any suggestions gratefully entertained!