Operating System problem.

Umm, okay, I have a Toshiba Satellite A505, and recently a new hard drive was put in because the old one stop working for some reason, but, the new hard drive doesn't have any operating system. The people, Geek Squad, said that I would have to reinstall it, but see I don't have the disk because it came with none. So, how would I go about this so I can at least boot up so I can fix this issue. I have another computer to work with, I just need as suggest as how to go about putting an OS on the laptop so I can upgrade to windows 7 or is there a way to just pop a CD inside my laptop and it start working. Cause currently, it doesn't seem to even boot CDs.