imac mac osx 10.0.3 privileges problems

This is the first mac I've had problems with. I cannot install any software, I can't edit privileges so that I can truly have administrator privileges, and I cannot mount any images. Basically so far this imac has been useless. I can't even backup the hard drive. I bought this imac so I can use it as a server. The imac is a 2001 or 2002 I don't know exactly what model another problem with this computer. I'm in the dark!! Help please!!

Erase and reinstall...........

Yeah its the sinplest way or get the password.

or if you had the installation discs you could just reset the password.