I would suggest calling an electrician. If you have an older house, those non grounded outlets probably only have old 2 conductor wiring, and there is no third ground wire available to properly ground the circuit. Overloading this type of outlet with modern, higher amp plug ins, could cause arcing problems in the outlet, and possible damage to the house system.
Consult a licensed electrician to get an estimate on switching those outlets to a true grounded, 3 prong circuit.
