I would give Ubuntu a try, beats the $hit out of M$ IMO. I can walk you through a mining configuration if you choose to do that.
That's simply not true.
I've tried mining on Windows 2003 x86/x64, Windows Vista x86, Windows 7 x64, Mac OS X 10.6.8, RHEL, CentOS and Ububtu.
I've noticed no correlation between OS and speed.
Though I've noticed straight correlation between mining speed and straightness of the hands ; )
Oh, and Mac OS X just sucks ; )