First off, sorry if this week is going to be filled with posts about the forum web part. It's popular and I just want to make sure everyone gets it, gets it installed, and gets it working in their environment.
There's some irregularity with adding the web part to a portal vs. a WSS site. The web part is designed for both but for some odd reason it behaves weirdly (yes, that's a technical term) when deployed to a portal (probably due to the fact that the user lists are different).
In any case, you might get an error loading the web part, but just refresh the page (by visiting the link again) where you deployed it and it should appear normally.
If you're an admin on a portal area and don't see the Admin option, email me and I'll send you info on how to access the list directly (if you haven't already figured it out) and you can edit yourself to be an admin (you still need update rights in that area to do this so it's not open).
Again, most of the issues are due to the fact that all actions in the web part (creating lists, adding/editing entries across multiple lists) are always done by the AppPool user and not the user in the system (although the Web Part keeps track of who you are and distinguishes between you and the AppPool user). This was done just because I didn't want you, the user, to have to maintain security on 5 different lists.
I think I made the right decision, but there's some fancy footwork that needs to be cleaned up here which will come in time.