Dang, I've only had this dreamcast for a week and I LOVE IT!!!

My question is, I'm trying to load Doom and Doom II (I have a couple hack versions too, like Alien doom). I actually have legal copies for the PC, but I don't understand how to get them to work on the Dreamcast. What is SBI? Is that something I need or want? There seems to be a couple different versions of Doom for the dreamcast, which requires real Doom files, is there one better than another to use with a gamepad?
Thanks for helping the newbie....this thing is awesome though!!!