Playing guitar hero I and II on a playstation 3...?

May be...

How can you play guitar hero I and II on a playstation 3? I talked to the people at gamestop and they said that I would need to buy a PS2 guitar plus a ps2 to ps3 adaptor, but I have some ps2 games that i play on my ps3 and every time it's loading it says to press the PS button, but there is no PS button on the adaptor. I haven't bought anything yet, but if you have any insight please help

There is a "menu" button on the side of the adapter to turn it on and afterwards the analog button works as PS