I used drupal 5 but not for real estate. Does your board allow you to use frames? That is by far the easiest thing to do, but I know I would get in BIG trouble for that.
Probably what I would do is check with the MLS and see what they allow and don't allow for idx listings and what tools they can provide you - Drupal is pretty easy to work with and edit/modify so hopefully that will get you started in the right direction without needing the modules...you could also contact that module developer and see if you could contribute to a 6.0 version...
OR easiest yet of all those things go to cnet.com and download the 5.0 version.
Good luck!