Richard is spot on. People criticise the reliability of Windows, but since Microsoft dropped the Win9x codestream (i.e. now we have Win2k and XP) the reliability of a maintained system on good hardware is IMHO as good as any Unix, and better than OS X (and I use all of the above
). Without wanting to restart the PC v Mac debate, and freely admitting I sit slightly on the Mac side, my main work XP/Pro PC has run 24/7 for 3 years, usually under serious processor and memory load, and has never crashed or locked up. The software it's running has gone from time to time, but it has never taken the OS with it. Linux is just as reliable, but OS X sometimes locks solid - and rather more frequently than i'd like.
The reliability problems are not helped one bit by the insecurity of windows, and I'm not going to try and defend that, but the main cause of unreliability in a clean system is cheap hardware and poor quality drivers - the two go hand in hand in my experience. Anybody selling decent hardware usually has the quality control to produce good drivers too. Windows should not just crash any more, so if it does there's a problem somewhere.