You can send and receive files over bluetooth out of the box on the N900. To send a file, go to the file manager and tap the file you want to send and select "share" (this is the translation from my german N900), select "send via bluetooth" and the device you would like to send the file to. For receiving files on the N900 you only have to make sure, that bluetooth is turned on in the first place.

Edit: This applies to PR1.2. If you are on a previous version, you could update to PR1.2 or use the standalone app "Petrovich", which works similarly to what I have described above.

Edit2: Sorry, after rereading your posting, I guess my answer is not really adequate, because you seem to search for a possibility to browse the filesystem or a shared folder of the other phone.