Cracking a forgoten password requires you to weigh the pro's and cons. You could use l0pht crack to attempt this, but if the password isnt a simple dictionary word it could take days to brute force it. You should go into it expecting the cracking process to take at least 72 hours.
Now, if the data is very valuable ( say a production file server ) then 72 hours is no big deal. The data is worth the effort.
If the data is just a bunch of apps you could re-install anyhow, then you may be better off just re-installing.
Decide which is the bettert route for you.