Where did you get the source *.vb files?
When I downloaded Forum_04.04.03_Source.zip (from sourcforge.net via link on DotNetNuke.com) and then unzipped the package, I only found a DotNetNuke.Modules.Forum.dll but no *.vb source files.
I checked a bunch of other modules, and so far, I've found source code only for the Survey and HTML modules....
So I'm very curious to know. Where did you find the source code for the Forum module?
Addendum added in Edit: I just found the source files.... Apparently, they're placed in another zip file labeled "Resources" within the zip file labeled "Source".