No idea how.
Id has been purchased by Bethesda software parent Zenimax. There'shttp://www.blogger.com/img/blank.gif a pretty good interview up on Kotaku about it but, basically, the statement from John Carmack is that id just had too much on it's plate.
They have an abundance of IP's that they can't really take advantage of properly and farming them out is getting hit and miss so this partnership will allow them to better make and distribute their games.
Overall it sounds logical, but I wonder if the sinking economic picture factored into the proceeding at all. After all, it's not exactly getting easier to do business and working under a parent company does offer a degree of protection. Especially one like Zenimax that plays host to two monster franchises like Fallout and Elder Scrolls already. Add Doom, Wolfenstein, and a bunch more and it's definitely a win for them- and probably for iD as well.
As long as they don't start getting rushed that is.