“There are numerous password crackers for the various Windows operating systems.”
I’ve never gotten any of them to work. On the other hand, UBCD4Win is a RAM-based operating system that includes elements of XP, and its password tool simply modifies the SAM hive file to replace whatever password exists with no password. This has ALWAYS worked for me.
I’ll tell you the truth... the last time I had to do something like this, I booted the machine with a copy of Backtrack Linux and brute force cracked the passwords using tools in the distro (John The Ripper). But this is beyond most “normal” users. I usually avoid any and all Windows operating systems at every possible opportunity. :-)