It will help. However, sometimes back while working a Communication company, with a very advance lightning protection system, a few millions worth of equipment were damaged due to the strike. Accordingly to experts, it actually came underground and hit the equipt as the surge can come from km away!
So it is best to off the PC when the weather is threatening.
erm... turning off is one... if you leave it plugged to the socket, there's still a chance of it frying... happened to my PC last time... its all about how well the arrestor system is build around ur area...
P&S: Sony U20, Pana-leica FZ5, Canon S90, Pana DMC-T3
SLR: Nikkor F60, Oly E-510, Oly E-5