I found a nice video tutorial on how to control Servo motor with Raspberry Pi here:

However, Raspberry Pi does less well in controlling the servos because Raspberry Pi is not a real time system compared to Arduino. Here is a link to the forum thread discussing about whether a Gertboard is needed in controlling a servo motor. The conclusion that I drew from there is that using a Gertboard is an advantage and since I already have it, I should use it.

Most of the online tutorials on controlling servo motors using Gertboard are using the older version of Gertboard. I am not too sure of the differences (other than assembled) between the older version and newer version and whether the those Gertboard in the tutorials has already included Atmel AVR microcontroller. Here is the best reference source so far.

Watch this video:

Other reference links:

I guess I need external DC power sources and may be some other circuits as well. Hmm, I am not good at this as I do not practise designing circuit since I graduated from polytechnic. 😦

There is also something new called Gertduino which combines the functionality of Arduino and Gertboard.

Servos under consideration:
TowerProSG90 (as suggested in the first video)