You might try using that voltmeter (eh, multimeter) to connect up to the softpot with a resistance reading setting higher than the spec of the softpot. Two of the lines should give you an open reading (infinite resistance), two should give you the reading of the max value of the softpot. With those readings, you should be able to figure out which leads are for what (ie, which is wiper and which are for voltage/ground) without burning it up.
Now, as for what to do about keeping it from burning up - there should be some clues in the spec sheet; usually a resistor of a certain size is needed (as mentioned by someone) - but I would think the "output" would be after that resistor, with the wiper of the softpot connected to ground as well. So you would always measure the value of the extra resistor at minimum on the output.
Thinking something like (sorry for bad ascii art!):
100 ohm Softpot
5V ----///----+-----//////////------ GND
| ^
| |
| +------------- GND
|
Output to Arduino