Can I reinstall Windows 7 using a pirated cd, but real cd key? [duplicate]

There's no need to pirate; you can download the ISOs for Windows 7 installation media directly from Microsoft (well, okay, Digital River's hosting the download but whatever), free of charge.

32-bit Windows 7 Home Premium

64-bit Windows 7 Home Premium

32-bit Windows 7 Professional

64-bit Windows 7 Professional

Links taken from here. I can't personally confirm they're live, but I've done this in the past and they look the same as I remember.

EDIT: Removed Ultimate links since they appear to be dead, but they're out there. Somebody feel free to comment and/or edit these in.

That would work however this is what Microsoft recommends.

This is what Microsoft recommends