not to boot that XP was any good, because it wasnt ahahaha because hacking into XP is well should not be classed as hacking as you just boot into safe mode ahahahaha...
Umm did you have a .NET account registered on the system?
I believe there is a way to bypass your account by using this account... just a hit and miss...
the alternative way is to reinstall windows in a new partition but always backup your data before trying anything you are not familiar with...
I have many ways around this just like DBD79 has but... it seems you may not be experienced enough to try any of them
no offence meant there but... my guess you were not quite SOBER while changing your password lol
why dont you try typing it again and try having numlock on or off Maybe your problem lies there?
EDIT
typos
Just clarifying... yes I meant your Win7 system... XP was a joke
And umm by backup I meant if you have an external hard drive you could IMAGE the drive onto for safe sakes