Can "Program Files" be installed on D drive? Raid 0 query.

I've noticed that during the installation of some programs (especially
Microsoft ones) it gets plunked down into C:\Program Files and there is
nothing you can do about it except to possibly move it after the install
and test it for reliability. Most of the time it won't work elsewhere.
Yet people often recommend installing the operating system on C and
Program Files on another hard drive. I'm not sure if it would be the same
if it was on another partition of the same hard drive as C. Or they are
saying to install as many programs off of C as possible? Here's an
example.
http://www.tomshardware.com/forum/24...ta-64bit-drive
I'm trying to decide how much space I need considering that hard drives
don't perform if they are almost full. And Raid 0 is a hassle. I want to
use small 7200 rpm Sata drives in a multi-hard drive setup to see how the
speed improves. I haven't decided if I'll use software raid or opt for a
hardware card.