Everytime you use Random, you in effect seed a new value in the word variable RandomValue. You only want the bottom two bits (to give you your four possible values) so extract them... Use those bits to illuminate your LED's... simple...

Code:
	LEDA var PortB.0
	LEDB var PortB.1
	LEDC var PortB.2
	LEDD var PortB.3

	RandomValue var WORD
	LEDValue var BYTE

Start:
	Low LEDA
	Low LEDB
	Low LEDC
	Low LEDD

	Random RandomValue
	LEDValue=RandomValue & $03

	If LEDValue=0 then High LEDA
	If LEDValue=1 then High LEDB
	If LEDValue=2 then High LEDC
	If LEDValue=3 then High LEDD

	Pause 1000
	Goto Start
This will give you one-of-four Random selection forever. I haven't got PBC but I'm sure you could convert it simply...