BG Pooh, you have one error in your formulas; the first line should read:

Q = center frequency / (band-width); looks like you forgot to type the ' / '

Also, the band width is determined by the 3 dB up or down points. That is, if you are boosting, where the filter shape curve gains the signal in frequency by 3 dB, or if you are cutting where the filter shape curve attenuates, in frequency by 3 dB.

Wikipedia has a nice image here:
http://upload.wikimedia.org/wikipedia/en/thumb/f/f6/Bandwidth.svg/350px-Bandwidth.svg.png

-Scott