|yeh, I just used your exact syntax, and we're both running xp, and mine worked.|
i did notice this however:
wmic useraccount where name='user'call rename name='newusername'
having no space between 'user' and call, generated "invalid inquiry".
wmic useraccount where name='%1' call rename name='%2'
(apologies for my former post: i cut/pasted your code, hence it still contained the error of no space).