It might be a bit too late, since the current version of Moodle is no longer 1.4+, but I thought I'd post the tool anyway It was developed as a Master's Project at SFSU. It transfers announcements, documents (items, external links, assignments), quizzes, surveys, and gradebook. You can watch a demo at http://188.8.131.52/ctt/ctt_demo/ctt_demo.html (be sure to turn ON the sound). To download the tool, go to http://184.108.40.206/ctt/bb_to_md.zip. bb_to_md.zip contains the source code, a PPT presentation (ms_talk.ppt), which might answer a lot of your questions, a technical report, ms_report.doc, which contains a detailed description of the project, etc. Oh, take a look at docs/README/README.html if you think you want to install the tool.
Please note that the tool might require more testing before use.
P.S.1 I bet it is possible to upgrade the tool to perform transfers between BB 6.1 and Moodle 1.5. If the overall structure of the Moodle backup archive stayed the same, then the fix should be done in the XSL files.
P.S.2 Let me know if you are interested in trying out the tool online. I can try to set it up on-line.