Not exactly sure what you mean by windows not being a realtime system but there is going to be some miniscule delay no matter how you display your data.
So if you want something to display 'exactly' as it happens it's never going to happen. So assuming this isn't what you want, you can go about it several ways. I am pretty sure the fastest is going to be to output to a parallel segmented or LCD display. This eliminates any serial comms and would be the fastest. However, it's kinda pointless since you couldn't actually read any data as fast as it would change it if it is changing faster than serial comms allow for. So the absolute easiest way is to use hyperterminal on your PC and send the data serially to the PC. This isn't going to be fancy but it will show you data. You could also build an app in Processing for displaying data. The next fastest is to use Serial segmented or LCD display which is more compact since it requires fewer connections. It is also arguably easier to program. Another method would be to use a graphical LCD but this would probably be the slowest method since there is a lot of overhead needed for displaying data on this type of display
Any of those methods are going to be fast enough to read. It really comes down to where you need to display the data. You could even write a program in Visual Studio using VB,C#,C++ etc that would display your data along with other functionality similar to processing.