I would try removing the battery, extended RAM, and airport, and then immediately reset the PMU and PRAM. I have seen machines with Airports that were not fully seated causing a machine to always boot into single user mode, so removing all extraneous devices and then resetting the machine should rule that out.
Other than that, I agree with Remacberlin -- boot your machine in target mode, and see if you can wipe your drive from another Mac. Sometimes a bad hard drive, or a drive that won't "unmount" can make a computer behave in non-standard ways, so if you can manage to wipe it, you'll be ruling the drive out as the problem.
If you need install media to reload your system, it's all readily available on...uh...popular download sites.