Try this untested code, it should do what your after...
Code:
temp.x = (integer((random(384)-192)/32)*32)+16;
temp.y = (integer((random(384)-192)/32)*32)+16;
temp.z = 340;
myObject = ent_create("physics_test.mdl",temp,NULL);


(if its not too late of course)

"There is no fate but what WE make." - CEO Cyberdyne Systems Corp.
A8.30.5 Commercial