Does anyone know how? Guessing the easiest way would be with an emulator?

But the gameboy up to a microphone.

line-in.

the same, if your game had a sound test i think it's the better way ^^

but don't use microphone (mono) preferer the line-in (stereo).

Good luck!

Yes.... Music ripping for Handhelds is significantly easier than for most consoles.

All you need to do is plug in the HEADPHONE from your handheld into the line-in or microphone input of your computer.

That, being the theory, is simple enough. To put into practice a little trickier.
The first problem is "Where do I find something that connects my handheld's headhphone to my computer?"

Radio Shack (or any electronics store) Specifically, you need a cable that has an 1/8th inch male plug on both ends. That's it, specifically, that's all the hardware you need besides the computer and the handheld. Trust me, these are cheeeeeeeeeap.

The software end : you need a program that can record input from your line-in or microphone. There's a bajillion of these on the interwebz, but if you need a place to look, I say try download.com and search for "sound recorder" or similar, and look for stuff with free-to-use licenses.

Here's a few things you're gonna need to contend with :
Sometimes sound recording programs come with an in-program way to do the sound settings, but chances are you're gonna have to set up your microphone through your computer. On Windows, you open up your volume controls, and you can set up your recording settings through that.

Secondly, you're gonna need to read the help file for the programs, as they're all different. I say this because you're gonna need to make sure you get good recording settings. It doesn't matter WHAT quality you initially record it in, or what format (but higher bitrate/hz is ALWAYS better, and .wav is usually the easiest to work with for an initial recording) But what you end up encoding the files to (the files you end up sharing with everyone). The preferred file format is MP3, and the settings you should consider are anything between 170Kbits-320Kbits and make sure to encode your music as VBR (instead of CBR) This will cut down on size and keep the same quality. Some programs are simpler than others, some are harder to use... I don't know what to say besides read the help :)

Oh, and some tips with your ripping :
1.) Try to do it through a sound select menu.
2.) If possible, try to get a collection of sound effects as separate file.
3.) If you wanna go all-pro, include some album art, or make a cover (however, most people don't really care about this)

Well, good luck with your recording. I look forward to your releases :D