I'm doing some research into an unfortunate matter I'm trying to sort out, so I'd be greatful if yous could help me out soon by answering some of my questions.

Does having 2 Yabb (CGI) forums on the same host run up a high bandwidth level or effect the bandwidth in any way?

Could two small community Yabb forums on the same host some how, run up 10 - 25 GB Bnadwith anyhow? (By small, I mean naturally 3 GB of transfer each.)

There may be more to come...

I don't quite get what you're asking. By having 2 forums instead of 1 then your bandwidth usage would go up.

Also check out the PHP/MySQL port of it as it uses less bandwidth and fewer server resources. http://www.yabb.info

I think Yabb is looked at as a more resource intensive script. I'm not sure about whether it consumes more actual BW, or not.

Yes im pretty sure YaBB just hogs up more resources, the BW is the same as other softwares, as far as I know.