To the best of my knowledge, you can't "retrieve" the administrator password, but you can reset it with something like Trinity Rescue Disk (or a good number of other free utilities), be careful what you use though, not all of them work.
If you have XP professional and you have another administrative account you can reset the password from the management console.
If it is you only account you need (as MrLinux) said a boot cd like erd commander or other utility to reset your password.