Forgot the passowrd

Hello,

i having a issue that i cant login my user in xp .can You tell me the exactly what to do .i have created only single user and i dont want to format.
Any other reason which makes my work easier .Ome more thing i need a security when ever in my absence some one using my system . I can know what they do the work With details.

Can it is possible in xp.

Thanking You
Nitil Kumar Tiwari