Well I live the UK and all my system dates are in UK format, so for those of you (like me) who need it simple:
MOVE "c:\myfile.txt" "c:\myfile_%date:~0,2%-%date:~3,2%-%date:~6,4%_%time:~0,2%-%time:~3,2%-%time:~6,2%-%time:~9,2%.txt"
The line above will RENAME "c:\myfile.txt" to "myfile_24-11-2004_12-48-04-39.txt"
Hope this helps someone else.
PS - can't find the old thread, mentioned above.