Currently iChat is the only client that I know of that allows more than two (up to 4) individuals to a video conference.
Skype does not allow this ... yet. But might in the future.
If I had a business where I had 4 widely separated individuals who needed to video conference on a regular basis cheaply, I would be tempted to purchase 4 low end iMacs and run iChat for this purpose.
Another option would be to purchase 3 cheap PCs for each location and on each PC have Skype installed. So each PC would be connect to one of the other 3 individuals. Not a clean solution, but it would work.
If I had to connect 7 people, I could to it with 2 iMacs at each location or 6 PCs. Again, I would choose the iMac solution.
Other than this, the only systems I know are the quarter million and above type that require numerous Internet lines and have remote control cameras and such. Definitely an expensive way to go.