I'd agree with Richard and drauk. For work I use Linux, Windows XP and Windows 2000 (on decent hardware) and I've never seen any of them crash. Ever. At home we have two Macs (OS X Panther) which I think are brilliant - far better for general ease of use than any other operating system I have used - but the reliability isn't close to my work machines. I see them crash or lock up every couple of weeks, despite being used much less.
I have, however, seen plenty of Windows crashes on machines with cheap hardware and/or poor quality drivers (in my experience the two usually go together). As Richard says, I would look there first.