On the first working day of January 1999 big institutional investors throughout euroland will wake up to find that they are no longer limited to holding domestic equities. But how do you go about swapping a national stock portfolio for an Emu-wide one? You can't just call your broker and sell half your portfolio. There are derivatives - options on pan-European indices, equity swaps and reverse convertibles - that can provide exposure quickly and simply. Or you can speak to the specialist portfolio traders - the guys who have quietly spent the last couple of years installing computer systems to process huge order volumes.