What components should I get?

[Yuhaney]

The video above is about AMD's latest CPU released in 2011.
Phenom II X4 is one or two years older than the FX 8120 which wouldn't in most cases even beat the Intel's i5 2500K.

But as said before: Choosing is completely up to you!
Make sure to check some other reviews about i5 2500K and Phenom II X4 before purchase so you know what you pay for.

Both do not include the Windows 7 software, but I reckon I can re-use the disk which I had for my laptop, (If this isn't possible please let me know)

You can use the same CD, yes.
But in case your Windows version is OEM (which I think it is, since you talk about laptop) you need to buy another license key or otherwise you break the EULA.