Just a power amp, turntable and speakers?

Nope. Generally, the TT needs a phono preamp and you also need a volume control somewhere. Get both in a preamp.

Kal

No, you need at least a phono preamp with a volume control.
(Very few phono preamps have volume controls, which is why most people, myself included, have a preamp with either phono boards, or a seperate phono preamp.) The phono preamp is also necessary to correct the cartridge's signal. It comes out of the cartridge with a RIAA std. phono curve signal, which needs to be corrected, or else the sound would not be a flat frequency curve.

Hope that helps, (and I am sure you will get a lot better, and more detailed explaination from others on this site.)

you could get an amp with volume control, but you will still need a phono-pre. You could do an integrated, although i do not know it any integrateds have phono stages.