From my own experience and noo paid influence, I would have to suggest the cheapest dreamhost.com hosting package they have [maybe just buy one years worth to test it out for cheap] - the main reason is that moving from iWeb to something like the setup desired will be a bit of a leap... Dreamhost offers something called 'one click installs' on their behind the scenes control panel. Part of that one-click install offers is both WordPress + phpBB [as mentioned above + i would throw my vote towards]. They are almost too easy to install.. however I would google and research as much as you can on how to make them hacker/exploitation safe - since out of the box all of the directories, files, ect. are named the exact same as elsewhere on the web - making them a target for the mischievous.
