to get the genesis emulator working, donwload the genemu file from the emulator section of this site, then copy this to the gpmm folder. Next create a folder in gpmm called "Genesis". Put your genesis roms in there. some roms don't work though so you might need to try a few. For your pc game, do you mean pc engine games or what? could u specify please.
ok, for the scumm thing, u can only play older lucasarts games. I recomend starting with "day of the tentacle". If you dont actually own it then i would never reccomend downloading it off kazaa as this would be unethical (ahem). Once u have the game ready, download scumm. Try the 132mhz version first as this will deffinately work on your gp and maybe try the high clock speed versions later. First copy the sc132mhz.fxe file to the gpmm directory. then copy the entire game (in this case Day of the tentacle) to a directory on your gp. Id recomend making a new folder in the gpmm folder and copying the game into there. Once the copying is complete load up the scumm program in ur gp and take it to the place you put your game. And thats it . write back if u have any problems.