regex for twitter style URL

Hi I am trying to do a mod_rewrite for twitter style username urls to http://myurl.com/andyjarrett would go to http://myurl.com/index.cfm?user=andyjarrett So far I have RewriteRule ^(((?!user|index.cfm))*.?)*$ index.cfm?user=$1 [L,QSA] But this just isnt working. Anyone done this or can help? Thanks, Andy Jarrett www.andyjarrett.co.uk