By animating I assume turning them on and off , the speed, number, spin etc. if you do it in an action ( i usually do it right in th chor) you adjust the settings of the sprites where the material is applied to the model/group. In an action lets say you wanted to turn the sprites on at a certain time you find the sprite setting in the material where it is applied to the model in the action then set the emission rate to 0% move ahead to the frame right before you want it on and set it to 0% again the the next frame set it to 100% etc . You can control this also by setting the interpolation mode to hold etc.
tried to show in picture
also watch sprite tut on ftp
ftp://ftp.hashmirror.com/pub/misc/sprites_tute/
particlesprites.mov