I want to setup my camera as an alternative to iSight

i have a video camera that hooks up to my macbook via USB, and when i go to record something in iMovie '08 or HD it only shows iSight, i've tried but can't seem to be able to set it up as an alternative to iSight, I don't really want to replace it, but when i hook up my camera, i want a feed from my camera to my laptop through my USB.



Is this possible? and if so, do i need new software, or is there an easier trick with the software i already have?



Please respond, posts with helpful info will be greatly appreciated, ths



711eman711