I use Joomla myself and find that it's pretty well up to the job AND it's free. I would recommend having a good look at additional plugins that are available from the joomla site as well. You will need to get up to speed with the php code for building your own template if there is not a canned solution on the net. I believe there is an extension for dreamweaver to help with this, although I tend to do most of mine on the back of a fag packet.
Micks suggestion is worth a look as well, I cannot comment myself as I have little experience with wordpress. Here is a list of open source php cms, the good, the bad, and the very ugly:
LINKY. What I would say, is do not even think about using Typo3. Not unless you want to learn typoscript, spend 6 months installing it, become a social out cast, and die before ever getting it to do something usefull.
I use joomla for my own web site and I would think it to your advantage if you can do the community web site in joomla, and offer additional bespoke web design to the B+Bs listed on your portal also in joomla.
Just to throw the cat among the pigeons, I'm looking at converting my own site to flash. It's no good for your purposes, but for a bespoke B+B site like mine, I get total control over the design and placement of content that html/css alone cannot give me. By using xml for the content, I can also make it seo friendly and easy to edit. I will probably run this in tandem with a none flash version on a permanent basis. Not as burdensome as one might think, when both versions of the site are complete, I will have one set of content files (xml) to drive them both.
John
Tony Benn...
"Most things in life are moments of pleasure and a lifetime of embarrassment; photography is a moment of embarrassment and a lifetime of pleasure."