Well, you could do it a number of ways. You could:
-use a portal and modify around it (we use the
board3 phpbb3 portal and it's pretty easy to modify, but there are others)
-use a mod like
Topics Anywhere (I used to use it and it was pretty easy to modify too, but I don't know if there's a phpbb3 version, that one is for phpbb2, I did see requests for a phpbb3 one though so maybe someone finally made it)
-use some of the code from a portal or other mod and put it on your site
-write your own from scratch.
It sounds like you're not up to the last one (nor would I be), but I'm pretty sure I've seen some leagues do it. Maybe someone from one of them will chime in.