Microsoft said Wednesday that the new games will double the size of the Xbox 360 game library, to 1,000 games. The new service is expected to launch by the end of the year.
To distribute a game on the Xbox Live service, game creators must use Microsoft's XNA Game Studio software or be an XNA Creators Club member. Each game will be vetted for quality and appropriateness.
Microsoft also announced that game developers also will be able to build games for Microsoft's Zune digital media players.