Guitar Freaks Controller
The closest thing I have used is the Dance dance revolution pad in epsxe and using the guitar hero guitar in guitar hero on PCSX2 For the pad I just used it as a direct input controller (that is what most if not all adapters will create) and just mapped the inputs like a controller. For the guitar I used lilypad plugin (version 0.12.1) set to guitar mode and set the guitar in the pad tab.
Peripheral manufacturer claims that RedOctane actually swiped its design from another company's Guitar Freaks controller. Guitar Freaks Arcade Style controller 5/5:). Honestly, I have had NO problems with this controller. I have been playing Guitar Freaks for 8 years now. Working Designs attempted to bring Guitar Freaks PlayStation 2 games in the U.S., but patent problems with the guitar controller prevented the project from moving.
Guitar Freaks Arcade Machine
As far as adapters go I used Kiky X-Series Playstation to PC Adapter but I dont think it is easily found anymore and the company and driver website have vanished off into the ether, but it worked for me using the default windows 7 drivers (though others have had issues) - The stepmania community is really really really really really particular about pads and adapters so this is a reasonable if not overly particular.