If it's an instrument or PA amp it will be 1/4" but hi-fi amps are most likely going to be phono (RCA) connections. Mine is all DIN but that is a rarity. Adapters and cables should be easy to come by.
Typically your pc end is going to be a male 3.5mm stereo mini-jack to plug into the Line Out socket and at the other end red and white male RCA connectors to plug into the Aux Input sockets of the amp (assumed you are wanting stereo). What is in between depends on what you can get at the store.
Re Radio Shack, in these parts it's now The Source, by Circuit City. Everything is now in flashy wrapping and twice the price. Same old staff. "I want an amplifier to match my speakers?", "Yes sir, and what colour would that be?"
Starman*