I once had the problem that I changed some settings in windows which disabled my automatic login into windows xp. I was prompted to enter my login details and could not remember them at all. The following method could be working in this and similar cases. You could try using the default Administrator login and leave the password blank. This should work for every computer where the admin password has not been changed.
Password Recovery Speeds
Now this is an interesting analysis of password recovery speeds. It compares password length and chars used to the time different computers need to bruteforce the password, ranging from Class A (speed of a pentium 100) to Class F (supercomputers, large scale distribution) computers.
Password resetting and recovering techniques
There are several methods to reset and recover your windows administrators password. The fastest method is to use a freeware tool like Offline NT Password & Registry Editor or the linux live distribution Austrumi.
Ophcrack 2.0 Windows Password Recovery
Ophcrack is a Windows password cracker based on a time-memory trade-off using rainbow tables. This is a new variant of Hellman’s original trade-off, with better performance. It recovers 99.9% of alphanumeric passwords in seconds.
