http://www.microsoft.com/windows/win...uirements.aspx
If you want to run Windows 7 on your PC, here's what it takes:
*
1 gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor
*
1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)
*
16 GB available hard disk space (32-bit) or 20 GB (64-bit)
*
DirectX 9 graphics device with WDDM 1.0 or higher driver
So even
this $75 CPU would be able to run Windows 7.