If you’ve got Guitar Hero and recently acquired Rock Band from say…Christmas then you’ve probably wanted to bridge the two together for a complete bi-gaming experience. Since Activision and Harmonix will never come to minds on hardware connectivity and interface you’ll have to resort to the Ant Commandos converter to make the two play nice.

The converter has a USB connector on one end and PS2 connector on the other. Simply plug the converter into PS3, connect the PS2 controller, and set the switch to either Guitar Hero, Rock Band or Gamepad and you are ready to go.
TAC’s Universal PS2-to-PS3 Converter is compatible with PS3 Rock Band and PS2 / PS3 GHIII, and it works with basically every PS2 axe you can think of, wired and wireless.
The PS2 to PS3 converter product page.
Source: Engadget.