Nearly missed this one, but with the launch of ISA 2006 and its impending RTM, an RC build of ISA 2006 is now available.
I'm running the previous beta as a web proxy with no complications; I'm looking forward to seeing what's in the new build. I'm also kinda hoping to get back to using it as an edge server again (i.e. with multi-NIC support) once the hardware becomes available at home...