You are correct, it is not a difficult challenge. But you do have to be careful.
The BRI side is easy. Just set up the BRI interface to accept a Multilink PPP call. The PRI side is a little trickier, you will find it easier to use dialer profiles for all PRI calls, both inbound and outbound, so each can be configured independently. The ppp multilink command includes an option to limit the maximum number of calls to two.
Search www.cisco.com using the keywords "dialer profile" and "example" for a wide range of sample configurations at least one of which will probably apply to your specific needs. Sorry I can't be more specific, because there is insufficient detail as to what else you need to support (routing protocol, dial-in/dial-out from/to other destinations, IP addressing, support for other protocols, budget, etc.)
Good luck and have fun!
Vincent C Jones
www.networkingunlimited.com