I live in an older home where the wireing is not the best. When the ac turns on the lights dim a bit. I need something to help with the ups and downs not get to my pc.
Either a double conversion or a line-interactive UPS with AVR will prevent a voltage dip from damaging your electronics. Even then, the line-interactive type usually won't regulate until the voltage is around 100 volts. I have a hard time believing that your air conditioning is causing a massive, computer-frying brownout in your house, though.
I don't understand what your problem is... is your computer crashing when the AC starts up, or are you afraid it will? If you elaborate on what the situation is, perhaps more people would be willing to respond to you. Have you taken any voltmeter measurements? Has an electrician looked over your AC and house wiring?