Do you have your iLife disk?
What OS version do you use?
Let us know
If you click th eapple logo and click about this mac it will tell you what OS version you are using, However i fit is that new you will have Leopard.
If you download Pacifist from here http://www.charlessoft.com/ it will alow you to easily restore your iMovie from the 2nd restore disk using the instructions from here http://www.charlessoft.com/Pacifist_Documentation/English/index.html
Let me know if you have any issues.