It depends on what is locked. If it is Windows then, as has been said, do a new installation.
If is is a password in the ThinkPad's hardware, there are two possible passwords. One can be reset and the other can't. (See the manual on www.lenovo.com.) This is on order to turn stolen ThinkPads into scrap.)
If it is the disk drive password then you will need to replace the disk drive.
T
May 2012
A used computer, made around 2003, that you just bough? In this case, it would be much easier to just whipe out the drive and do a fresh installation.
I'd use Windows XP, Windows 7 or any distro of Linux.
Stay away from Windows Vista as it's more resources hungry than 7...
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix notebooks/laptop pcs.