The WiSheild library's take a lot of memory.
If you are using a 168 it might not have the room.
Even the 328 could struggle if you try to do to much but I would have thought there would be room for and lcd library.
Pin 8 is selectable by the jumpers on the WiShield.
Have you got the jumper in the correct position?
"# Switchable interrupt pin usage between INT0 (port D, pin 2) and digital pin 8 (port B, pin 0)
Switchable LED on digital pin 9 (port B, pin 1) "
From http://asynclabs.com/wiki/index.php?title=WiShield_1.0
Also have you tried the LCD on its own without the WiShield?
Can the Arduino power both devices?
Or do you need to look at an extra power supply for the LCD?
Gordon