Sega has announced that they will be bringing out popular titles from their past consoles (Genesis, Saturn and Dreamcast) onto the Xbox. According to forum grumblings, it's still not certain if these games will be updated for the Xbox hardware or if they'll be packed together onto compilation discs or even if they'll be released outside of Japan. Sega will be outsourcing the responsibility to Coolnet Entertainment. More details as they become available.
News source: Team Xbox