just plug your phone to PC and use fastboot (follow the link sent by kanded) that will work.
monty...you can't just use fastboot! it will not work till HBOOT is updated! s-off users dont have this option.
follow my post here http://xdaforums.com/showthread.php?t=1467060
to allow you access to the htc unlock, which then allows you to install cwm 5, until then...you cannot!
so please stop telling people with s-off things you cannot do!
ive said it loads of times now! you s-off users have it easy. took me ages with help to figure a workaround just to install cwm 5.