Microsoft had released the latest version of ISA server couple of months ago and it has undergone a name change. The new release is named Forefront Threat Management Gateway (TMG) 2010. This version supports running Exchange Edge 2010 and Forefront Protection For Exchange 2010 along with it in the same box.
I bet you know where I am heading! You don’t need different servers like in the old times. You can have a couple of servers in the DMZ with all three components. The same box will publish Exchange services like OWA, OA & ActiveSync and at the same time act as the first layer of defence for incoming emails.
TMG provides central management for Exchange Edge and Forefront Protection 2010 for Exchange when located on the same server. It does not include either Exchange or Forefront Protection 2010 for Exchange. Both must be purchased and installed separately. TMG 2010 also comes with a long list of new features.
Install TMG, Edge 2010 & then Forefront Protection. Make sure you update the scanning engines & enable all antispam & antivirus filters before connecting it to production network.
Check this article for installation steps.