just get a XBOX controller, an old usb cable, cut the controller cable on teh end, connect the usb cable (joo dont even need 2 solder, just twist and tape) then dload teh xbox pc driver and plugitin and j00 got a dreamcast controller on dah pc for ch$ap
I' m using a GC Pad with a usb adaptator and no problem. I have not instal the drivers of the adaptator because it crash the emul.
This adaptator work with all emuls i have test (with dolphin i use JoyToKey and it work great).
You can find here : http://hp.vector.co.jp/authors/VA016823/joytokey/english.html