Yep SD showed you how already. Sorry was off Teaching an Excel class today so no time to look at the board this morning.
Well with a single built-in controller and only 2 drives it really doesn't matter that much on the partitions.
You could have easily used the whole thing but having a separate drive for SHARES and DATA is a good thing. You can modify the root of the D: volume for more locked down permissions (though 2003 is much better than any previous version for that already)
As for "stability" no not an issue. I have a 600GB RAID0 at home that runs just perfectly.
Now if you have more controllers and more hard drives then YES it could make a big difference how they're setup.
Sound like you've got it going already though so cheers