I recently got my first build up and running and I am just about to install Windows 7. The thing is, I bought it OEM, and I've heard it is a one time use thing? I want to install it on my current HDD, but I plan on getting an SSD later. Can I still install the Windows I bought on it even after I've installed it on my HDD?
OEM can only be used once PER MOTHERBOARD. You will be fine. Samsung SSD's come with migration software that allows you to transfer everything without having to re-install windows.
I have a 256gb 840 pro and its awesome.
As stated above, you will be fine. There is also plenty of free software that can do the job if you don't get a samsung SSD. Also I would like to state that I hate microsoft's license policy. If they didn't basicly have a monopoly on the market no one would have this single install per motherboard BS.