tangor - 9:33 pm on Sep 17, 2010 (gmt 0) [edited by: tangor at 9:54 pm (utc) on Sep 17, 2010]
Unless things have changed, the E-Blah folks will (for a very slight fee) install the software for you (the software itself is free).
There are quite a few good ones out there, the list above contains some very well-liked and commonly used forum softwares.
Usually it is not the software that is the chore, it is the management and community building that takes both time and decision making.
[edited by: tangor at 9:54 pm (utc) on Sep 17, 2010]