lost administrator password

i need the administrator password of my computer. i can only log in as a guest. I have ophcrack installed and was wondering what the best way is to obtain admin hashes.
If i use the http://loginrecovery.com/ will this get me the password to my admin account of the hashes necessary to run through ophcrack?
And if i go throught mycomputer/manage/user/admin and reset this what information will i lose? i have some necessary information and files that i cannot lose.
I have windows XP,
please help me.