Now you have the local admin password for that computer, if the computer has a standard XP or 2000 login screen, login to that computer as a local admin.
You are now going to need Cain availible on this site here. Install it to your Flash Drive or put the setup file on your Flash Drive and install it to that computer. (Not reccomended, and make sure to destroy any evidence afterwards)
Once you have Cain up and running you will need to click onto the Cracker tab and then MSCache (10 usernames and passwords will be cached from previous domain logons). Hit the plus sign near the top and let it dmp the files from Local System. It will then proceed to cracking them which may take a while.
If you have any problems with this Tutorial please let me know in this thread.
Hope this can help you!
