On Fri, 25 Nov 2011 08:30:41 -0600, wrote:

They sell some sort of device that you plug a portable MP3 into it,
and that thing sends the music to a blank radio frequency so the mp3
player can be heard on the car radio.

What are these things called?

I'd like to get one, but dont have a clue what to shop for. I asked a
guy in the electronics dept at Walmart and he could not figure out
what I wanted. (Of course I didn't expect anyone with knowledge at
Walmart), but thought I'd try. I suppose this is something to buy
online, or maybe Radio Shack...

But first I need to know what they're called....

What you're looking for is a "modulator" or "FM modulator". Be warned that
they don't work very well in large cities (too many FM stations) or on long
trips (stations change). I'd like one that's tied directly into the antenna
lead (so it would override any local station) but haven't found one yet.

About $7 from Deal Extreme or usually about $30 locally.

http://s.dealextreme.com/search/modulator