If it ever happens to you that you need to restart old computer which you have not logged on for 2-3 months and you find out you have no clue what the password could be, do not panick. Exactly this happened to me yesterday. Fortunately I have remembered reading something on lifehacker few days ago about bootable CD which contains live Linux distribution with password cracking open source software Ophcrack. It runs from CD only, does not touch your file system, only loads local SAM and tries cracking the hashes. And boy, it works !
I downloaded and burned the ISO and rebooted the old Windows box. It had the password in less than 8 minutes. Then, just out of curiosity, I booted up my Windows notebook which I use for one of the projects with the crack CD. On this notebook I use fairly reasonable password, 9 characters, combination of uppercase, lowercase and numbers, which is not valid word in any language (to avoid dictionary attacks). About two minutes after boot and start the notebook fan started to go full speed, a clear signal that the 3.2 GHz Pentium 4 HT works like crazy. The password was cracked in 18 minutes.
This thing is pretty scary, if you consider all possibilities.