Here's Microsoft's marketing schpeel on the differences between the different versions of Windows 7:
http://www.microsoft.com/windows/windows-7/compare/default.aspx
My guess is the reason OSU-COM recommends Windows 7 pro is for the more robust networking features and perhaps for the WinXP compatability mode.
As for system requirements, hardware has WAY outpaced software these days. Any run-of-the-mill computer today should be able to handle most software for the next 4 years (unless you are looking at hard core gaming or video editing/rendering). With that in mind a system should have a minimum of two processing cores (Core 2 Duo, i7, etc.) at 2.2GHz or more processor speed , 4GB of system memory, 250GB or more hard drive (recommend more if the laptop is going to be your primary computer). Most laptops share memory with the video card, so keep that in mind when making system memory choices. Hope this helps.