In terms of installing it on the domain like vbulletin is installed on websitebabble.com, no you can't. But you can use SBI!'s service InfinIt! to map a forum to your site. In other words, the forum would have to be hosted elsewhere and InfinIt! will allow you to map the forum to your domain name so it will look as if it resides on your SBI! domain.
I may have some of the terminology wrong but the gist of it is, no you cannot physically install a forum on SBI!'s server.
__________________
Don't put the cart before the horse. Plan your website, thencreate it.
Hmmm.... now that's a question for the SBI! support folks or their forums. I guess it depends on how the engines view a CNAME. Because ultimately that's what you're doing when you use their InfinIt! feature. You are mapping your forum to your domain by updating the CNAME.
Good question though. Any other SBIers know?
__________________
Don't put the cart before the horse. Plan your website, thencreate it.
That is a great question, as I just used Name Park It (thru SBI) to purchase quotesgab.com for my forum that I would like to launch this fall, but I want the traffic to be attributed to quotesinsight.com ....Hmmmm...I'm going to go poke around SBI forums....will keep you all posted.