Hi,
I have successfully setup a laptop with dual graphics to work under arch. Mind you, "work" in its most basic form : only the integrated GPU is enabled, and only the Opensource drivers are involved. As far as Catalyst is concerned, Arch doesn't have fglrx in its main repo, but in AUR (sort of like a PPA). So fglrx support can be considered semi-official. They however do have great wiki entries (I guess you haven't looked hard enough
) :
Arch Catalyst. In AUR there is a nice package : catalyst-total-pxp. This is a version of catalyst with
powerexpress enabled. This should give you what you need. I haven't tried it.
Serafean