Picturetel came out with a complete system they called IPower about 18 months ago - it has proprietary hardware and software that makes it the best product on the market, IMHO. We used it to do exactly what you are talking about - video,collaboration,whiteboarding with powerpoint slides, you name it - from Thailand to the US - and it was an outstanding success. And the price - this is what will blow you away - about $10,000 dollars US for a a single complete station - camera, speakers, IPowerbox - everything but the LCD projector (that would be entirely up to you).
Did I mention we did it over 128K bandwith - with heavy traffic, and lots of networks delays? Don't know what kind of algorithms they use to control the delay on the network (its proprietary and frankly I didn't care) but it worked great!! We had Picturetel in a head to head competition with Polycom - PictureTel won hands down for all the reasons I mentioned above.
With five managers at five site at once, you will probably need a H.323 Multi Control Unit (MCU) or a Gatekeeper of some kind on the network somewhere - get together with your local Cisco CSE to find out - the stuff we used from Cisco cost around $30,000 but we had more sites - the problem is thatyou can only connect 4 Picturetel IPowers together without a MCU.
Your total cost with the Picturetel/Cisco solution for the scenario above - my best guess - $80 to 90 thousand US dollars. It may sound expensive - but its a WHOLE lot cheaper than about 3 years ago.
Hope this helps.