Infrared TV Remote to Arduino
The most common (not sure what others are used) carrier frequency is 38khz. You need an IR receiver tuned to that frequency to get the signal from the remove. See this page for way more information.

There is no encryption or special receivers needed as long as the carrier frequencies match.

That's really all the hardware you need. On the software side of things, you read this signal and decode it. There's a neat little library for doing exactly that. It's called Arduino IRemote.

It even has an example sketch which tells you just what the decoded value is of whatever button you pressed so you can use that in your other programs.