As a operating systems junkie, i don't see much difference in the both the OS. Both OSes provide all the functionality with respect to -

security (ACLs being absent in Windows, that one difference)

Multiuser/Multitasking and Multithreading

Robust memory management in both

Device management

Process management

and so on. (Pretty much all the OS feature which one studies in OS 101)

The only difference i can think of with respect to enterprise OS capability of unix and windows, i have seen Windows run only on Intel processors and power PCs to some extent. But Unix and its new buddy linux can run on practically all the zillion hardware platform making it the most proliferated OS ever.

Long live UNIX...