I like the idea! A friend of mine has actually made something like it,although with Visual Basic and not in 3D , if you finish it don't forget to show it to us!!! BTW don't worry about the lameasses who will crack this very original idea of yours, since your not the only one who has thought about it....
Hey, this is a cool idea. As far as the pysics go, cells "attack" in several ways.
Some use phaygocytosis (engulfing another cell)
some use a method where they penetrate the cell wall and insert a capsule that bursts and releases harmful chemicals
others bind to specific sites on the cell and transform it
and many others . .
I am not sure how much the A6 physics engine would help with this, but I haven't used it very much. It seems like you would need to do a lot of scripting, but it is still a fun concept.
This is not really a physics scripting question, so I'm moving it to General Topics.
Btw: There isn't anything crackpot about this idea. A few years ago somebody was using A5 to do an anti-body simulation (I remember because they were using very small high polygon models which is why we added the “clip_size” value).