Well nothing from your old computer will be usable since everything in your list is newer technology. Since your current processor is AM2 socket and the mobo you got there is AM3 socket unless you get an AM2 compatible mobo. But then again if you plan on gaming your processor might bottleneck your GPU, hence decreasing your preformance in video games.
Heres something i found to save you some money
GPU - http://www.newegg.com/Product/Produc...-309-_-Product
CPU/MOBO - Newegg.com - Computer Parts, PC Components, Laptop Computers, LED LCD TV, Digital Cameras and more!
(saves you like 26$)
You wont be able to use much out of your old computer except maybe your Hard-Drive , Media Reader, Optical Drive. thats about it.
Well once you build your computer you would have to install all the drivers to gain internet access again, if your router has dhcp on you should be fine with getting internet automatically once you install the NIC drivers
Im not expert but this is my advice, im pretty sure theres members here willing to take it a step further.