i forgot windows xp password.....

i have very important data in that computer....i am not get the solution for this...please can anyone help me in this....

i have searced in the net and downloaded the "active password changer" software.....i installed this in my computer...it is showing the user accounts but when i am trying to reset the password...it is asking me to buy that software........can anyone show me the solution...please... i have very important data in that computer.if possible u can mail me on [ santu78j | at | indiatimes.com.......tHANK YOU BYE