There are multiple ways of looking at this, I suspect you are just looking at modeling your team concept with Custom objects.

If so, then you'd create a couple of objects here - one for the team and another for the members.

You would then be able to create a tab for the team records and under that you would see the members using our standard related list functionality.

Getting the activities is going to be a tricky one though because the system isn't really set up for this and depending on how you have sharing configured across the system and the role hierarchy, i.e. is the "team manager" always above the team members in the role hierarchy?  Maybe the way sharing is enforced is just how you want it.

As you learn more about sharing in the system you'll understand more of what I mean above.

To actually show the activities for the team members across the system you would have a few options I think. First, you could link to an activity report from each member record. Depending on what edition to which  you are subscribed you could write an scontrol that queries the API for the activities and presents it inline. Lastly, and my favorite ;-), would be to utilize visualforce to build this interface which would be the best from a performance and ease-of-building perspective.  Of course visualforce is in developer preview only right now. To learn more about that check out the webinar on Tuesday.

If you want to pursue the scontrol or visualforce routes I highly recommend checking out the force.com cookbook as it has great examples and tutorials to get you started.

Good luck and welcome aboard!