The method that was recomended to me, and I really find effective, is to place your new arrivals in a 2-3g bucket (or rubbermaid, or whatever) take a longer piece of air-line, with a gang valve or some other method of controling the flow, and use it as a syphon, creating a steady drip into the bucket.
Empty excess as required, after a few hours, your fish will be acclimated to the temp/water in your tank. Then its a simple matter of netting the fish and adding to the tank. Be careful not to get the net near the bottom of the 'holding' tank, so that you dont pick up any unwanted debris/eggs/etc.
I somehow got MTS snails in my angelfish tank, still trying to figure out where the heck they came from! Don't figure I'll ever get rid of them now, vacuuming today, I found at least 100...
Andy