A full working system will require even more resources. If these requirements are satisfied, you still have to determine if all the pieces of your machine are compatible. If you have a network card with a 3Com 3c501 chip, NT can't talk to it. And these are just samples of some possible compatibility problems. The full list changes often.
Incompatibilities constantly recede as better hardware support is added.
But a constant stream of new, incompatible hardware is always hitting the market. Well, The PC hardware market has few solid standards. IBM-compatible hasn't really meant anything since IBM stopped leading the industry. Companies which do this are rare, but you'll save trouble by seeking one out. Let them find the best hardware to fit the operating system you want.