don't know if there exist a better way...
switch (integer(random(4)))
{
case 0:
snd_play...
case 1:
snd_play...
...
[EDIT]
you can also use snd_create and a text-element to call the sounds randomly..
something like this:
my_sound = snd_create((all_sounds.pstring)[integer(random(num_sounds))]);
snd_play(my_sound,100,50);
(not tested!!!)