I'm not a Frontpage extension expert nor am I a fan. With the extensions installed and just working on a server that had the extensions and that was it (as in, no PHP or scripting), whenever me and a buddy of mine would update a subsection of a site (it was just a subdirectory of the main site) we would kill the entire site because Frontpage had this thing with indexing files and because we didn't use Frontpage to upload the pages, Frontpage freaked out and brought the site down.
This wasn't our idea of a fun time so we found another web host who could give us scripting and I stay away from Frontpage extensions whenever possible (and both sites have been much more stable since we branched off).
I think (and I'm not sure on this) if you continue to upload files using Frontpage on your forums site (assuming you install the extensions on it), you may be ok.
But my thought process would be to leave the extensions off and save the hassle of the extensions freaking out. I guess it depends on what you need them for...
