New disk for Mac Mini

Hi'

Planning a switch from an old Core2 Duo PC to (Windows 7) to a Mac Mini (i7) where a new SSD and extra RAM are to be installed.

But when the SSD drive is replaced the OS disappear.

So how do you get an OS on the new hard drive (Windows or Mountain Lion) ?

PS! does the Lexar USB 3 CF readr work with the Mac Mini ?

Thank you for answers.

// Silkeborg