QUESTION:
 If it rained on Neptune, would it rain helium or something  else?

ANSWER from Heidi Hammel on April 25th,1996:
If it rained anything on Neptune, it would probably methane up in the
upper atmosphere, or deeper down, it might be water.  I think a more
likely thing to happen on Neptune, though, is snow storms.  But 
instead
of water snow like on Earth, Neptune would have methane snow.
Heidi