if you re look over your program....

loop:
high PortB.0
low PortB.0
goto loop
PAUSE 500

imagine that the lines are being processed and scanned in less than micro seconds, you send portb.0 high, then microseconds later you are telling it to turn off. now that output is on for micro seconds, but our eyes react way to slow to beable to see this. so yes the program is working, but do as whats been done in the above post and put in a pause between the highs, and lows

Chris