Make taxonomy items sortable and groupable

Say, I got 5 taxonomy items on the subscriptions page:

- item 1
- item 2
- item 3
- item 4
- item 5

I d like to show following to the user:

=================================================

Group 1:
- item 4
- item 3

Group 2:
- item 5
- item 1
- item 2

=======================================

I guess this will never provided by the module itself. Could you give me a hint how to do this?

For the items be sortable and groupable, I d have to save a group id and a rank id somewhere, so I think this wont be trivial.

Any hints for me?