Apologies for the very short reply above, I was texting it from the bus on the way home from work last night. Yep the good news is that this project is very do-able Ive made a few arduino projects communicating to the N900 over Bluetooth, although not using a minipro board. As long as it has (and it should have) the correct pins for the Bluetooth module (TX, RX,..) you'll be golden.

Speaking of which, what type of module did you buy? I use a BlueSMiRF and it's pretty well straightforward. Depending on your experience of soldering, the only tricky bit to setting it up is soldering in 6 pins so you can connect it to the breadboard/or your own socket etc. When it arrives it wont have a connector, but you'll see 6 holes at the bottom of the module where these pins should be soldered. What i did was take a row of male-male header pins, snip off a row of 6 so they're still connected to each other, bent them at right angles, and soldered the pins on one side to the 6 pin hole contacts of the module. Bending at right angles means I can push the other side of the pins directly into the breadboard while keeping the module vertically upright.

The second trick to BlueSMiRF is pairing the module to the N900. You probably wont get the shared password/pin with it, so to save you searching around it is "default". You connect via the N900, search for bluetooth connections, pick the BlueSMiRF, and "default" will be your security pin. You'll see the red led on the module turn to green when connected.

You already have python sketches for reading/writing and there'll be Arduino examples all over the net. You should be able to find what you need there.

The only other type I can think of might save you hours of frustration If your arduino is running a previous bluetooth sketch and you want to upload a new one, you may find that it will fail to upload - probably because the BlueSMiRF module is busy doing it's thing. The trick is to remove the power to it so the module isnt running then upload the sketch and reattach the power.

I'll be interested to know how your project goes, keep us updated