How to change an admin password in XP/Vista

Let's say your flatmate changed the password on the admin account. Let's say you're not trying to hack into his personal files to see naked pictures of his girlfriend ..rather you're trying to install a vital piece of software that you need to test so as not to get fired. What can you do?

First option
In case you have another administrator account ..well ..use that ( duuuuh).

Second option
You might be able to get into safe mode. It may be protected or it may not be. If you do get into safe mode you'll be able to create another account with administrative rights and then log on to that one. To get into safe mode just press F8 while booting and select Safe Mode.

Third option
If you somehow have access to system files. WinXp ,actually windows NT, stores passwords in crypted files : SAM. There are plenty of .sam editing tools out there but I wouldn't know which one to recommend. You can also try deleting the SAM and SAM.log files located in windows/system32/config/. The problem with tempering with these files is that even a tiny mistake may make your windows unsable and you'll need a clean reinstall.

Fourth option
This actually is the safest one. You can use one of the many freeware programs out there that are specifically designed for this. For a list of such programs and a few other tips and ideeas you can take a look at Petri's site. I actually used Petter Nordahl-Hagen's Offline NT Password & Registry Editor downloaded from there and it worked wonders.
Hope this helped someone, cheers.