Is my usb drive unusable?

Once I mount my windows iso to my usb drive to install windows on my newly built computer can I format that drive and install a different iso on it, or once I do that is it just done? I want to take the usb that I installed win 8 on this computer and install ubuntu on my old one, with the same usb drive.

You can mount an ISO many times on a flash drive. I do it all the time.