Before I tell you about the Win7 calculator I want to let you know about a really neat alternative way of doing calculations on your PC.
If you have the Google Toolbar installed in your browser just type in the calculation into the search box. It will then give you the answer directly without even hitting <Enter>. Cool eh?
And it will do complex calculations as well, so tan(pi**2.7+e/sqrt(67))= works just as well as 2+2=.
It only works in this seamless smanner with the Google Toolbar though. If you use a normal Google search box you will need to hit <Enter> to evoke the standard Google Calculator. You can find full details on the Google Calculator here.
Back to the new fancy looking Windows 7 calculator. Apart from looking great and doing all the normal calculator functions it will convert units, has a scientific mode and statistics mode as well as a new programmer mode. In fact, just about everything you need.
To install the Win7 calculator in Vista follow the instructions here:
You can't install the Win7 calculator in XP but you can install this look-alike. Unfortunately it doesn't have the full functionality as the real Win7 calculator but it does look a lot better than the standard XP version.
If you use XP and want more functionality you could try Microsoft Calculator Plus or use one of these freebies: