So, you've been asked to reboot in safe mode, and (oh crap!) you don't know the administrator password! Never fear! Prajna is here! You will need to get a tool called tweakUI for XP. Please download and install it from here. This is a Microsoft product used to enhance windows functioning. Once downloaded and installed, run the program (Start -> Program Files -> Powertoys for Windows XP -> Tweak UI).
Now, click on the logon word in the tree on the left, click on "Show Administrator on Welcome Screen", click on apply, then close this for now.
Now go to start -> settings -> Control Panel, and find the User Accounts icon and double click it.
The user account page will look something like this:
Select Administrator. You are presented with with options to change its password or change is picture. Select change password. Set the password to whatever you want it to be.
Finally, open Tweak UI back up, click on logon, UNCHECK the "Show Administrator on Welcome Screen", click apply and close. You now have set the password of Administrator to something you know so you can add/remove programs you need to properly in safe mode.