The very basic liability that you'd be undertaking would for the condition of the equipment. If the equipment malfunctioned or broke down, and as a result of that incident, a person was injured, you could be held liable for the damges and/or injuries.
From a strictly risk management point of view, the best way to avoid liability is to not rent it out at all. If you want to do this to make a little money, you'd better get some insurance. You'd also want to have the individual sign a rental agreement that states that any damage that is incurred while the renter is using the equipment is the responsibility of the renter, etc.
Remember when you're protecting yourself, the best way is to eliminate the liability completely by not getting involved in the activity. If you can't do that, then figure out a way to transfer the liability to someone else (rental agreements, hold harmless agreements, etc.). If you can't do that, then you have to accept the liability, but do it at the absolutely lowest level that you can (the amount of your deductible for your insurance policy).
Good luck! /w3tcompact/icons/wink.gif/w3tcompact/icons/grin.gif