Place an object as a child of the emitter to have it emitted. You can place a null under the emitter and then various object inside the null to have the various objects emitted randomly. This is assuming that you're using the standard particles (not Thinking Particles), which is what it sounds like you've got going.
For the collision effects I'd advise you to download the free Fizz plugin. It handles particle-object and particle-particle collision, and it can even spawn new particles from collisions. You can get it here:
http://www.bonkers.de/download/downloads.html
It may not come with a manual, due to some kind of flap between the programmer (David O'Reilly) and the plugin's former distributor, but if you download the plugin *demo* from Plugin Cafe it comes with a .pdf manual. :) Fizz used to cost over $100 but David graciously made it freeware after R8 was released.
