I use the Canon 350D and Sigma 70-300 APO. There is a picture I took with it in the
Gallery section birds/tits and finches (chaffinch in flight).
I am only fairly new but here is what I do.
I use TV mode and set the shutter speed to 1000.
With such a fast shutter speed I compensate by using ISO 800 unless it is really sunny in which case I drop to 400.
I reccomend doing what I am to start with and capture the pictures on a predictable flight path which in the case posted was the bird table. I sat out side at the patio focused on the feeder and with camera on above settings plus multi shot simply waited for a bird to fly in towards the feeder. The shots are all hand held (not easy with that lens but still more than happy with the outcome. I guess the shutter speed also takes out some of the shake.) Once you get used to the settings and the confidence is built up (nothing worse than spending time on a shoot only to find they are all too dark or too bright) then from there build your knowledge and experiment more with the other options. I am sure some of the other suggestions are as good if not better but this is what has worked for me and with the same lens as you have.