Aye its just no fun at the moment and the following is just off the top of my head; There is a cookcomputing dll version conflict if your using the latest version of YAF and MojoPortal; I recompiled MojoPortal using the same versions as YAF.
You need the YAF.Mojo.Dll which provides the URLBuilder for YAF in MojoBuilder (this is what you were looking at in the SVN), it needs to be compiled.
You then need to create a .ascx user control file with using the MojoPortal Module Control to inherit from, and have the <YAF:Forum> tag within that control; or like Bbobb says on the other thread use a .aspx and link the masterpages.
You have to integrate the web.configs.
Follow the same steps for placing YAF within MojoPortal as you would a subfolder i.e. app.config or user.config (if you included the app.config ones in there) settings.
I'm putting in some work to try and help people along with MojoPortal integration; however I am not finished and not sure when I'll have the time to put it together.

"It's a case of RTFM.. the only problem being we don't have a manual!"
When I post
FP:Mek in a topic, I'm leaving my footprint there so I can track it once I get into coding/supporting. (Yes I stole this off Ederon

)