If you are ok with CentOS/RHEL, there is a scalable way to boot multiple machines simulataneously using ........ bittorrent !

http://www.rocksclusters.org/rocks-doc/papers/two-pager/pape...

Rocks is used at production cluster installations with thousands of servers.

http://www.rocksclusters.org/rocks-register/index.php?sortby...