questions on SMP/duals/parallel

[dinamica at webcable.com.br]

Hi there,

I'm new to this list so pls, forgive me if these sound dumb, but here we go:

If i understood well the SMP support in the kernel allows you to run kernel process in parallel (ie between your two processor in a dual Xeon/MP AMD) but not user jobs, is it correct? (pls, could you suggest didatical references/www on SMP features :-)) 

To run a user job (eg. my own coded app.) in parallel in a dual, one node system, i still need some kind of message passing code, right? This would be diferent from running it in parallel in a cluster/various (single processor) nodes, since in the dual its a shared memory computing and in the later it is a distributed memory?
 
Ok, so why are you guys running dual clusters? One direct benefit seems to be able to split user job in one proc. and kernel proc in the other (what SMP can do, can't it?). But are you splitting a user job between a dual (shared mem) and various nodes (dist. mem)? Which are the benefits? Am i missing something?

Thanks a lot for your time,

Guilherme