'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