Tabs to move user in and out of usergroups

[iBaker]

Hi
Just wondering whether the following concept could be done and also if it is workable in terms of database loads etc.

I have a site that caters to different types of areas in one main area - say for example boating as the main area and sub areas of dingy, speed boats, yachts etc

There are 10 generic forums that are applicable to all the areas like General Discussion, Weather etc.

All users are in the principle usergroup of Registered users. Each sub area has its own usergroup like Dingy users, Speed Boat Users etc that have their own group of extra forums

This means that a user sees the 10 generic forums assigned to the principle usergroup of registered users at the top of their page and blocks of forums applicable to the public joinable secondary usergroups that they have selected. The problem is that some people who are interested in all types of boating get a page with 150 + forums on it which is to much.

My thought was to somehow after the 10 generic forums to have images like tabs for a user to select which sub area of the forums they want to see from that point down.

The way of doing this I thought would be that when a user clicks on a tab image they are removed from all secondary usergroups and then joined to the secondary usergroup that corresponds to the tab that they have selected and the forums that are assigned to that usergroup are then shown and with the generic forums above it.

Hope this makes sense - I am not even sure if this method is the right way to achieve what I need - is there another way that is better - your advice on whether this can be done efficiently and how to do it or other options would be appreciated greatly - thanks!