word2000 extension identification dilema

Word 2000 with sr-1 and sp-1 updates in lace along with trying to reinstall and then uninstall and reinstall have not worked. Saving a document results in the error of word saying someone else has my file open or the user does not have permission to write to the file. The file gets saved by changing its name and the orig file has the extension added .in2 to the existing document. I’ve searched MS sites and the help and found no reference to such an extension. I found a freeware “fileext.zip” that did not id the extension type. Also no viruses found. Any help would be greatly appreciated. This problem is sporatic. Thanks.