I though this was so important I thought I list this twice.

I came across a Dreamcast emulation site that not only has mame roms already adapted to use on the Dreamcast. But also has emulators I swear you will not find anywhere else. Like one for 7800, Lynx, Playstation 1 and Intellivision. The 7800 emulator runs at 95%.

http://imrtechnology.ngemu.com