MacSoft has posted Halo 1.05.3 which is for the English retail version of Halo only and restores Mac/PC play. According to MacSoft, the Macintosh code has been synchronized with version 1.05 of the PC code (Build 610). Gamers with the new NVIDIA 6800 video hardware may play Halo using either the NV Shaders or ATI Pixel Shaders modes.
More info and download link here.