Heres where you can download the game and the emulator to run it.(you need to download the emulator)
I reccomend that you get the NoCash Emulator...just so you can use the Pokemon:Green Version and the Pokemon:Yellow(Pikachu)Version
The Yellow Version is the best, Pikachu follows you around!
Downloads
The Pokemon Emulator!!!!
Pokemon Game Editing thingy
Pokemon:Red Version!!!!!!
Pokemon:Blue Version!!!!!!
Pokemon:Blue Version!!!!!!with 149 pokemon at the beginning of the game(including MEW)
The NoCash Emulator
Pokemon:Green Version(Japanese)
Pokemon:Yellow (Pikachu) Version (Japanese