When you click on "
Download and Pricing" and see the column labeled Download IPB, goto the bottom of that hello box and right below "Purchase for Download Now" in small text is a link called "[ Free Trial Version Information ]" that link will take you to the page to download IPB for free.
IPB used to always be free, now they are pushing a paid service with more support things of that nature. However the paid version and Free trial are the exact same message board, no changes what so ever.
A few things I like about IPB over phpBB is the admin panel - I spend a lot more time in the admin panel on a forum then I do in the forum itself. Also IPB has a VERY extensive hacks/ mods forum, not nearly like vBulletin but a very nice selection for a free message board. The standard layout of IPB I feel is much better then phpBB. phpBB is old and hasn't changed a whole lot, they promise to have a new version out soon but that's been sometime ago. IPB is also working on a new version that looks pretty promising and their forums are running the beta versions of it now.
Either way both of these message boards will be perfect for a small to medium message board and you can't beat the price. If you're forum is a medium to large message board I'd HIGHLY recommend dropping the cash to purchase a license of vBulletin - the development and support teams are top notch, the software rocks ( just look at RCNT

), and the amount of hacks/mods are endless with vBulletin and if a mod isn't released yet you can VERY easily find a programmer that can make it for you.
-Michael