"steve marchant" schrieb
Having difficulty with seeing any difference between
the two terms.Can anyone offer definitions, both
generally and in relation to, say, microprocessors.


http://dictionary.reference.com/search?q=emulator
tells me (among other definitions):

Computer Science. To imitate the function of (another system), as by
modifications to hardware or software that allow the imitating
system to accept the same data, execute the same programs, and
achieve the same results as the imitated system.

whereas the search for simulator returns:

One that simulates, especially an apparatus that generates test
conditions approximating actual or operational conditions.


For me, the important thing that the emulator tries to
have the same usefulnesss to an user as the "real" thing.

For example, think of a terminal that ***emulates*** a
VT-100 terminal. Nobody has a VT-100 simulator.

HTH
Martin