I haven't (yet) changed my steering wheel, but as far as I know, you're going to need a car-specific hub. These are relatively available for momo steering wheels, but less common (??) for Nardi and smaller companies. A Nismo steering wheel should (again, "??") bolt right up.
However, what you CAN get for Nardis (etc) is a nardi--> momo converter, which allows you to use the momo hub.
This shouldn't be a hard swap provided you've got all the tools (a couple wrenches?) and parts (steering wheel, hub, necessary hardware). All I've heard is that you may have some trouble getting the original wheel off; just use some force. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>