is it finals week? :-)
you can download the manual for keylight at here:
http://www.thefoundry.co.uk/pkg_overview.aspx?ui=A5FB8E97-D752-4E01-AC7D-17...
but basically you can use the despill bias to set a color to better remove the spill color from... if that makes sense... generally, you'll often want to set the despill bias to a flesh tone to better remove spill from flesh tones, but you could choose any color from the foreground object that you are keying.
i've never used the alpha bias (well, never unlinked it from the despill bias) but it does the same for creating the key/alpha rather than the despill. you could try that if your key color was removing parts of the foreground object by selecting the color of the foreground object that was getting keyed out (you'd first have to disable the effect or set it to view source, then pick the color, then set the effect back and set the despill bias).
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW
