I started this project a while ago but only finished it now this idea has been done before but most people just cut a slot in some plywood and attach their circular saw, whereas i got a piece of MDF and attached it to a black and decker workmate, i cut a recess in it for my circular saw and screwed into place, i cut mitre slots in the top of the mdf so i can make jigs to attach to the saw (crosscut sled) then i made a custom clamp that tightens very hard to the table. Materials cost is around 35euro and it takes around 3 weekends of work and it works great. once done making it make some push sticks and a zero clearance insert which i still need to do. I will post some more pics on my page. Hope you try and make this, it works a treat.
-- Adam, Ireland, http://www.youtube.com/user/AdamTheWoodworker