How do I install software on my IMac without the master password?

I have an IMac (Mac OS X 10.5.5) but have forgotten the main password. Is there anyway of resetting it without reinstalling OS X (I’ve broken the disk, so can’t do this anyway!). And if I did reinstall OS X, would I have to reinstall all of the programs back on to the computer i.e. Photoshop, Illustrator etc?

Method 1: Take the computer to a neighbor who has a Mac, an Apple retail store, or a Mac service shop and ask them to boot it to an OS X DVD and reset the password. This can be done easily without reinstalling anything.

Method 2 (requires your knowing the short name of the user home folder):
Go to the first link below and follow the instructions. I didn’t put them in this answer space because the Yahoo Questions form limits line length AND “word” length, so the long commands get truncated with … in place of important parts.

Method 3 (will delete your user account and put all your user documents into a disk image):
Boot to single-user mode and:

Type “/sbin/mount -uw /”
Press Return. (Nothing appears to happens, no problem. Also, you will see # again. That’s fine; ignore it.)
Type “rm /var/db/.applesetupdone” (The normal format of Mac OS doesn’t care about upper case.)
Press Return.
Type “reboot”
Press Return. (Now stuff appears to happen. You will finally get past the “Welcome” in a dozen languages and then you can create a new admin user. It should be a different short name from your old user. A few screens later, you come to the registration. Just choose “later”. It doesn’t come back later to nag.

After you have completed the new user, open the Users folder and look for “Deleted Users”. It will have a mountable disk image that contains all your old documents.

Mac Apps 2011