I think you have a few errors in your code:

1. If you want to flash the LEDs on PORTB, you must make PORTB an output:

TRISB = 0

2. The first pattern of LEDS only has 7 bit, make it eight:

PORTB = %01111111

3. At the end, just befor the loop ' GOTO Main' you need another PAUSE 100 of the LEDS will change too fast to see.

So the Main bit of your code should look like:

DEFINE OSC 4
TRISB = 0
PORTB = 0

Main:
PORTB = %10101010
PAUSE 100
PORTB = %01010101
PAUSE 100
GOTO Main

END