How do I turn a Windows CD copy into a *valid* ISO?

Hi,
A long time ago I've made a copy->paste of my Windows 7 CD content into a special folder on my HD for backup purposes.

Now, when the backup is actualy needed (laptop screwy, CD lost) I discovered I don't know how make it bootable.

I've tried WINISO, Free ISO Creator, and some other program which eventualy yielded me an ISO image' however when I used
'WINDOWS 7 USB DOWNLOAD TOOL' it tells me that my ISO is not valid and when I try to make it bootable through WINISO it tells me that the file has no boot information.

How do I fix my image?
Thx.