Retail versions include both 32 and 64-bit media in the box. OEM is much cheaper, but remember that you can't move an OEM copy from one computer to another... it stays with the computer on which you first install it.
The retail copy would as well... if you were installing and using both computers. If you only activate it on one computer, then it should be fine.
December 28, 2009 1:30:16 PM
Here's the Wikipedia article on Microsoft Windows OEM licensing and there is a complete Windows 7 Edition comparison chart on the page showing the differences between OEM and Retail licensing for each version.