An easy way to do this is by duplicating the orginal head then on the duplicate adjust the eyebrows to where you want them to be at there highest then select the dup head then the org head and go to Animation/deformers/create blend shape. This will blend the 2 shapes togeather and create a slider in the blind shape window (window/animation editers/blend shape) that will allow you to move the eyebrows up and down. You can do this for as many expressions as you would like.

Hope this helps...

D.