It may be a lot of reading, but I try to go in simple detail about CPUs in my article and what stuff means.
Your CPU and modern games: A guide to those building.
Dual core means it has two logical cores to process information. When you go to task manager it shows two graphs.
GHz speed does not really mean much when you get into advanced architectures. It's kind of like an engine. You can have a 7.0 liter engine from the 60s but it may only produce 250HP without help (exaggerating for example). A newer 2 liter engine with a small turbo setup can produce closer to 400HP simply from upgrades and it's much smaller. Terrible analogy so just try to follow me. GHz is the speed at which your processor calculate information. Newer technologies incorporated into the architectural design allow a different CPU at the same speed to process things faster. For instance like I said before, a 3GHz Pentium 4 is MUCH slower than a 3GHz or even 2GHz Core 2 Duo. Understand? The speed also doesn't equate to age either. A Pentium 4 3GHz CPU could be found as early as 2003 I believe, and they still make 3GHz CPUs here 10 years later. Newegg won't lie about the hardware they have for sale. If it says 3Ghz Core 2 Duo, that's what you'll get.
In that case, the computer I linked you has what is a 3GHz Core 2 Duo E8400. I know for a fact it was made and released in 2008. There is only 1 other Core 2 Duo CPU that is a perfect 3GHz and that is an E6850 which was released in 2007, but was a high end chip for the time and not commonly found in any pre-built machine. You can find these specs here.
List of Intel Core 2 microprocessors - Wikipedia, the free encyclopedia
An easy, but not so opportune option for you would be to build your own rig. It would be more than the 164 but there is no way the software could come up with a specific "date" because everything would be different, but current.
Another easy way to bypass this is put a fresh install of Windows on there.