well... you can delete your account and it will ask if you want to delete all your files and folders... but i don't think you want to do that do you? hrmm, i think i need more coffee... i have a book here, perhaps i will look and see if i can find anything... yes...
go to my documents - tools - folder options - view - and scroll all the way to the bottom and uncheck simple file sharing and hit okay
log in as admin - log out of current user - at welcome screen hit ctrl-alt-del twice and log in as admin then go to the c drive - docu and settings and rename the folders
if that doesn't work then:
then go to the c drive - docu and settings - right click folder to be renamed - properties - security tab - advanced - owner tab - select user who you are logged in as - check replace owner on subcontainers and objects and hit apply - then rename the folders