Given the hardware you have, I'd recommend doing a clean install of Windows 2000 Professional if at all possible. W2K is a stable and mature OS that will run well on the hardware you have in hand and is fully supported by Microsoft (and will continue to be supported until at 2010 if I remember the MS roadmap correctly). If you can bump up the system RAM to 256 MB that would be great, but it'll run just fine on just 160 MB if you keep the number of startup processes and programs trim.
 
As already mentioned by other responders, WinXP requires more modern and robust hardware to run well and has no stability advantage over W2K. Win9x and WinMe should be crosssed off your list simply because, among many other reasons, they are no longer supported by Microsoft and have security vulnerability issues.
 
Installing W2K is ususally quite straightforward.: W2K Pro Build 2195 > Internet Explorer 6 Upgrade  W2K SP4 > approx. 50 or so hotfixes (unofficial SP5) and you'll be good to go for the life of the machine.
 
HTH ..
           Jeffrey Ottie

 		
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