Great Escape Games will have copies of their Clash of Empires rules available at Salute 2011.
From their announcement:
Clash of Empires rule books arrive at Great Escape Games HQ on April 14th, so we will have them at Salute on the 16th. The book is full colour, hardback and 192 pages. It is priced at £25. You can get in touch with us to reserve a copy, or you can talk to 1st Corps, Gripping Beast or Magister Militum who will likely be offering Clash of Empires army deals, as will we.
In the rulebook are lists for the Early Imperial Romans and their enemies in the West. The first army list book will cover Early Achaemenid Persia to the death of Alexander. Many army lists will be free to download from the web. They will be official, but will be living lists reviewed by us and the wargaming community. Some of these will go to print, but many will stay on the website as free downloads.
The rulebook also contains rules for four different scenarios, including elements such as terrain placement, terrain types, army initiative, and flanking maneuvers.
More details on our site.