Word2000 file slow to openin office 2003

Have many users recently migrated to Windows XP. They have office 2003 now. When trying to open past Word 2000 docs with Word 2003 it takes 3-5 minutes to come up. You can copy and paste it then into a new Word 2003 doc and it opens fine. We have thousands of documents in Word 2000 and need a remedy for this ASAP. Any help would be great!!