QUESTION:
What is the low-gain antenna, and where is it located?

ANSWER from FAQ:
The low-gain antenna is located on the tip of the cone (the "feed")
sticking up over the High Gain Antenna. It can transmit data at
rates up to 1,200 bits per second, comparable to a very slow home
modem (circa 1985). However, top transmission rate during orbital 
operations will be 160 bits per second (remember, Galileo will be much
further away from the Earth, so the data rate drops) 

There is a second low-gain antenna on the spacecraft--the long, thin
antenna that hangs off of the short boom that holds the radioisotope
thermoelectric generators--but it is stowed away permanently.