If you have CTRaidAssist, then you get AFK status shown in the tooltip.
As far as I know, there is no way for an addon to test if another player is AFK. You can parse the combat log for the 'You have gone AFK' message & work out if you are AFK, but you cant get the details of other raid members sadly. That means, to do the AFK for other people, you need a mod that broadcasts when that player goes AFK like CTRA does. I could add a similar thing to OzRaid, but unless everyone used OzRaid (woo!) it wouldnt work
Maybe one day Blizz will add an 'IsUnitAFK' function which would make it all much easier
