Hey brane1234, what phone do you have? If you have s60v3 phone don't use MeBoy to play games (it's bad emulator :D)
I myself have Nokia n81 8GB and I have NES, GB/GBC, SNES, GBA and Sega emulator on it.
And I can even play games via bluetooth in vNes, vBoy and vSun. (Haven't tried more than twice, traded Graveler with my friend and got Golem)
And now to your question. You can just download MeBoyBuilder.jar from it's homepage.
1. Get it from the site
2. Open it and push button Add Game
3. Find your game (you can put more than one but it doesn't work in every phone)
4. Then press Create MeBoy.jar and you have you're game
5. Move it to your phone
6. You're ready to play your game!!!