During one of my afternoon jaunts on the web, I stumbled on to this site while looking for conversions:
The author of the page has made one of the better RPG adaptations I've seen, even for a work in progress. There are rules for the specifics of the He-Man/She-Ra setting, the races you can play, and spell and class ideas. Even the worlds of the setting are described in D&D 3e planar rules. This is a blend of 3e rules and conventions blended with the MotU setting, and the author does a commendable job.
The character sections are currently small but interesting. There is plenty use of prestige classes in the character write-ups. Many characters are mere the name, alignment and what classes they are. The best part are the sheer amount of characters and monsters that the author has provided. You just don't get He-Man and Skeletor. You get stats for obscure MotU characters as Plundor the Despoiler (an evil rabbit) and Octavia (a green octopus lady from She-Ra). Pretty neat.
Check out this site if only to witness a really good RPG adaptation of the Masters of the Universe setting.