DOS is great, but might be a pain if your hardware isn't old. Unless your soundcard is "soundblaster" compatible, and the manufacturer has included DOS drivers, you'll have no sound. The video output will be 640x480 too. Almost all hardware needs it's own specific DOS driver to work under DOS, including USB devices.
Try one of the "tiny" flavors of Linux, and a Linux version of MAME, the learning curve will only be slightly higher than if you were trying to learn how to setup memory, soundcard, cdrom, and mouse dirvers in DOS with config.sys and autoexec.bat.
A third off the wall choice would be using a Win PE for either Vista or Win 7. Using WIAK and injecting your needed drivers and modifying the startup to run a single MAME game. It can run from CDROM or a USB, and will always run the same way because it runs an image from a RAMdrive and is read only. The learning curve for that is huge, and unless your CPU is 5GHZ it will be slower to boot than the other options.