I posted a photo of a black Netherland Dwarf anda black Polish below for comparison below.
The Netherland Dwarf is smaller, weighing under 2 1/2 pounds. The Polish can weigh up to 3 1/2 pounds.
The coats of the two breeds are very different. Netherland Dwarf is rollback, Polish is flyback.
The Polish have a very fine bone, where the Netherland Dwarf is medium to heavy in bone.
The ears are a little different. The Netherland's should be well rounded at the tips are are very thick. They don't necessarily have to touch together. The Polish ears should be held perfectly erect, touching all the way up. They generally aren't as thick as the Netherland Dwarf ears and aren't as rounded.
The head of the Netherland Dwarf is rounded in all directions. The Polish head is not rounded in all directions.
The eyes of the Polish should be very bold, and have more consideration in judging that the eyes of the Netherland Dwarf.
The Netherland Dwarf has a high head mount and it should sit up on the judging table, where the Polish has a very low head mount and is posed down on the table.
The Netherland Dwarf has nearly 30 show varieties (colors). The Polish only comes in 6 show colors.
The body of the Netherland Dwarf is a short, round ball. The Polish has a medium body with a slight taper to the shoulders like a commercial breed would have.
The UK Polish is very different from our American Polish. The UK Polish resembles our Britannia Petite.
Netherland Dwarf
http://www.andrc.com/winners.htm
Polish:
http://www.giveusahome.co.uk/breederspages/rabbitbreedpages/polish.jpg