Not while windwos XP is running. You would need to boot from another medium to do that. You can install the Recovery Console while booted into XP, then when the computer boots up you will have the option to boot into Windows XP or the Recovery console. From there you can run FIXMBR or FIXBOOT.
http://www.helpwithwindows.com/WindowsXP/howto-12.html
http://www.helpwithwindows.com/WindowsXP/howto-12.html
