Why does my Dell 570 have 2 CPUs?

If you're looking at "Two CPU's" from dxdiag.exe or Device Manager, it simply means your computer has two cores, aka "Two CPU's".
For example, here are screenshots from dxdiag and Device Manager from my computer :) I have a Quad Core so it says I have 4 CPU's.
phenomdxdiag.png
-From dxdiag
DeviceManager.png
-Device Manager

Oh and to answer your question, almost all CPU's nowadays have 32 bit and 64 bit capabilities. Just depends on you to choose the operating system :)