Here is my network configuration:
All my PC's connect to the Switch and the switch is connected to the router.

Router (Buffalo WZR2-G300N-10/100) --> Gigabit Switch (TRENDnet TEG-S80G 10/100/1000Mbps) --> PC 1, PC 2, PC 3, etc.

Now my question is, will I be able to get the gigabit speed when I copy files between my PCs or the network traffic has to go through the router and I will not be able to get gigabit speed.

Copying files between PCs will not involve the router, so theoretically you should get gigabit speeds.

In reality, you will get something less. Low-end routers like this do not handle full speed on every port simultaneously, so the other devices connected to the switch could harm transfer performance. Then there's the overhead of the transfer protocol that you are using. But you should still see speeds that are better than fast ethernet (100Mbps).

Do all of the computers have gigabit network adapters? If they do then you should get gigabit speed (keeping in mind what garsh posted). Otherwise you should get gigabit speed between the computers that have gigabit networks adapters & fast ethernet speed for those that have 10/100 network adapters. If any computer has just a 10Mbps adapter, well, time to upgrade (it's gonna go sloooow).

Yes, I have gigabit ethernet cards..

Thanks garsh and alan!!!