On a small scale you can do this with relatively low spec small computers behind a screen. You can then wirelessly managing the computers using remote tools
You can also using streaming media techniques (similar to what some do at home)
AV can be sent over CAT5 with specialist equipment
Wireless is possible although for several monitors streaming will be better than video senders
All of these would require some technical knowledge with pointers being available but you may well need some on site help to get up and running. Depending on budget a specialist provider would be an idea.
Try:
http://www.interactive-whiteboards.co.uk/digital_signage.htm or
http://www.displays4media.co.uk/prod1.asp?ID=214