Help Buying New Operating System (edit: solved)

Okay so I posted over a week ago that I was having computer troubles. Well it got worse. I tried to use the recovery partition on my laptop to bring it back to factory settings, but that failed and now when I start my computer it says bootmgr missing. I don't have a recovery disc and the partition is busted, so I don't think I have any other options, besides buy a recovery disc from Toshiba or just buy a windows disc.

So my question is. I'd like access to a copy of windows that I can transfer between multiple machines if need be. I might want to build a PC in the future so I might as well start by having an OS to use. I know there's something called OEM versions of windows, but when I research it some people say you can only use it on the first system you install on and some say that has changed with windows 8.

I'd like it to be a copy of windows 7, but if it's not going to be much cheaper I'll go with windows 8.

So, with all that said, what version of windows am I looking for? I appreciate your recommendations.

edit: installed the windows 10 preview on my computer. really liking the changes so far from using windows 7 all this time. Hopefully the upgrade process to the full version from the preview version is painless.

Once the version is no longer current (windows 7 and older), they don't care as much if you swap oem versions between computers, though you technically aren't supposed to.

I'd try out the windows 10 preview and see if that suits your needs, then just buy 10 when it comes out.

@kidavenger: is there a way to put the preview on a disc?

http://windows.microsoft.com/en-us/windows/preview-iso

"Swapping" is allowed in the case where like "restore from catastrophic failure" where the old machine died in a completely unrecoverable way so you get a new machine. This shows up at Microsoft when you activate it where as long as you haven't activated your license fifteen times it should be fine.

As a practical matter, you should get the OS as cheaply as possible. If your OEM version doesn't work any more then going for beta or other discount programs is the way to go.