Here's what the reply was (only part):
"Before you couldn't, now you can. Yes, you can absolutely do this as part of your Site Build It site.
Site Build It has a wonderful module called "Infin It!" which enables you to add forums, message boards, blogs, memebership sites, stores and so much more -- I guess that is why they called it Infit It
Think of your SBI! site as a C (Content) T (Traffic) P (Presell) motor. Infin It! enables you to plug third party resources into your SBI! site to amplify that motor with more content (ex., blogs or forums). And it enables you to harness that engine (i.e., get more dollars out of it!) by plugging in monetization models (ex., stores, membership sites). And here's the beauty of it all. Infin It! ("II!") lets you plug third-party resources (we'll call them plug-II!ns) into your site without sacrificing your brand, which you've worked hard to develop.
Whether it's a membership site, blog with TypePad or Wordpress, or a forum, or a wiki or a shopping cart system, or whether you need to host content on another site (MP3s or videos, or a database-driven system such as a directory), you can make it part of your SBI! site.
Infin It! opens up the SBI! architecture and lets you extend your SBI! site functionality with modules that are not “core” to C -> T -> P -> M.
Remember that SBI is a power house when it comes to building a site that will generate targeted traffic which in any business is the most important thing."