To remove the password: click start, run, type in REGEDIT, click ok, this opens registry editor. Click + in front of HKEY_LOCAL_MACHINE, + in front of SOFTWARE, + in front of Microsoft, + in front of Windows, + in front of Current Version, + in front of Policies, Click Ratings, look to right, Click line below Default, press delete, enter. Leave default line only in right pane. Close registry editor. Next click start, find, files and folders, type "ratings.pol" in top line, C: in bottom, find now. When this file is found, delete it. This will remove password set, and leave content advisor fully operable. Next time, chose a password you can remember.
To be truthful the contents advisor will not really stop your kids seeing all sorts of things. Education and awareness is much better.