Integrated amps have the pre-amp built in...so they can accept inputs from source components like CD players etc. power amps just amplify signals and send to speakers. If you were to plug a CD player into a power amp, the output strength to the amp wouldn't be enough. Pre-amp makes the signal strength sufficient.

If your receiver has pre-outs (can support an external amp) I'd go that way. If not, you need an integrated, or a pre-amp.

Check ebay and audiogon.com for great deals on used amps/integrateds.