'connect' user to categories through preferences

Hi,

The users on my website can create/update their account for newsletters
purposes. In my next-release i want to add more preferences, based on
activities(travel). The user can select categories(activities) through a
select box:

musea (a)
beach (b)
sports (c)
modern wonders (d)
trekking (e)
ect.

If activity a + e is selected the user is 'connected' to group A
If activity b + c is selected the user is 'connected' to group B
ect.

When i user is create or updated, the user is placed/connected in a
group based on their preferences. And based on the users categories i
want to serve different content.

Someone ideas links to guide me....(newbie..)

Grtz...remco