Word 2003 cannot open Word 2000 Documents!!!!

I have word documents created using Word 2000 SP3 which works fine on all
office 2000 PC.s but i am having a problem opening the document on office
2003. the following error appears:

Word experienced an error while trying to open this file
* The file may be corrupt try File/Open and Repair option
*check the file permissions of the documents or drive
*make sure there is sufficient free memory and disk space
*open the fiel with the text recovery converter

I have copied the file to memory stick and onto my desktop and there are no
permissions set.
There is over 120mb free memory so this should not be the problem.

We do not use Norton Antivirus, instead CA Antivirus. To test on different
environments I have removed the antivirus and firewalls from two pcs running
Word 2000 and Word 2003 and still get the same results as listed above.
MSFT Knowledgebase is worthless for this issue.
PLEASE CAN SOMEONE HELP!!!!!