I do not know about the search engine's user interface,
but maybe it would be easier to convince the document
submitters to add some "magic keyword" like MPEIX to the
MPE-related documents and thus be able to search for an
expression like "mykeyword AND MPEIX" ... assuming that
it allows to "and" keywords.

This might be an alternative to seperate databases...

Lars (how many docs would have to be converted?) ;-)