Corrupt Downloads and constant CRC errors

I'm looking for suggestions and ideas on how to stop receiving CRC errors and eliminate corrupt downloads.

System Specs:

Motherboard: Gigabyte G41M-ES2L
CPU: Intel Pentium Core Duo 5300 O'Ced to 3.0Ghz
Ram: 4GB G.Skill
HD: Seagate Barracuda 7200.12 1TB
Video: Sapphire ATI HD4850 1GB
O.S.: Windows 7 Home Premium 64 Bit

I have been having corrupt downloads and CRC issues when downloading online games and a few other things. The issues got so bad, I did a complete reinstall of Window on my reformated hard drive. Right away with the Windows updates, I once again started having issues. It would take me multiple attempts to download and install some updates. The very 1st thing I attempted to install on this system once I finished with Windows updates was Firefox 5 so that I could begin gathering all my driver updates, anti-virus, ect. I recieve an extraction fail, file corrupt error after downloading Firefox Setup 5.0.1

What's going on here? I am at a total loss. I have no other system issues. No lock-ups, no crashes, other than not being able to download and install programs my system performs very well.

I am suspecting an issue somewhere in my network connection. The following is a list of things I am thinking maybe the cause but I'm not sure how to trouble shoot each one so any advice would be greatly appreciated.

-My ISP: Frontier Communications (Formerly Verizon) of SW Michigan. I have had multiple outages and basically crap service from them since Frontier took over.

-My ISP provided router/modem: Westell model 7500

-My intergrated network card on my mother board

I mainly suspect my ISP as I stated the service and support form them has been absolute crap since late last summer, but without any other local options I'm stuck with them. On the plus side I've had so many issues and complained so much to them, I'm currently in the middle of a 6 month run of greatly reduced pricing.

Thanks very much in advance for any suggestions, tips, or advice.

It is most likely a hardware problem with your PC. The most likely problem is bad memory or the overclocking. Perform a full memory test and get back to us.

I like to use Memtest86. The free version works great. I use it on all my new builds to insure the memory is good.