I recently aquired a used rotel rx102 stereo receiver and onkyo cp101 A turntable. I bought a new stylus needle for my turntable, and plugged the turntable into the phono jacks on the receiver and from there into regular (not powered) speakers. The volume is very low. A Guitar Center rep told me over the phone I need a pre amp. I thought the phono jacks took care of that. Do I indeed need a preamp?

If the receiver doesn't have a function specifically named PHONO, yes. Very few AVR's have phono preamps. They're not expensive. I'd check eBay.

I'm sure that you've solved this by now, but this receiver has phono jacks for both ceramic and magnetic carts. You might have your turntable plugged into the incorrect jack. And, yes, if you have a phono input, you have a preamp.

Also, this isn't a very high-powered receiver (7 wpc or somewhere in that range); if you're using speakers that aren't very efficient, that could lead to low volume levels.