fatdan:It isn't XP really, XP uses far less resources than any of the newer OS's...
True, XP is the only OS I've ever been able to play this game with ease, have a smooth meter and have the meter stop, when I actually clicked the mouse. On an ancient PC (over 10 years old, with half a gig of RAM) with zero maintenance. Apart from clearing browser history on FF every 45 minutes since the issues with flash memory clogging up (last 6 months or so).
It's been next to impossible to play well on any other OS without tweaking, which I don't know how and I wouldn't bother learning it.