Windows XP Administrator Rights

Prior to upgrading my system from Windows 2000
Professional to Windows XP Professional, I had 2 seperate
accounts.
User
Administrator
After I upgraded my system to Windows XP Professtional,
my system automatically logs me on as the user. I can
not find a way to log on as the administrator. I need
administrator rights in order to delete one of my
registry files. I'm having difficulty in creating an XP
driver for my HP Photosmart 1000 printer. HP stated that
I might have a ghost device on my system since I did not
disconnect my printer during the installation process. HP
was trying to walk me through the process to delete the
file VID_03f0&PID_3003 so that I can try to reinstall the
XP driver again. They claim if this does not work, I
will have to reformat my drive and reinstall the
operating system.