Uname for Windows

Seems like a curious question for this group but I don't feel like
joining a Windows mailing list just to ask it. Besides, it's actually a
Samba question in disguise.

I was trying to add some Windows XP computers to a a domain and it just
wasn't working. I finally wised up to the fact that these computers
came preloaded with some crippled version of Windows called 'Home
Edition' even though the salesman had sold them to the poor business
owner as office machines. The OS had been customized with HP splash
screens and whatnot to the point where it was only obvious that it was
something like XP. I didn't really know that MS deliberately made
something crappier than Windows.

So how does one tell just by looking what version of Windows is running
on a machine?