All modern OSes use vector graphics. The big change in Windows Vista is it supports vector graphics which allow it to scale the image to match the screen in Pixels Per Inch.. In fact there are some 300 pixels per inch monitors out there.. In fact Vista lets you set your screen dpi..
If you want to see Windows technology that uses vector graphics you need to look no further than WPF graphics which is completely vector based...
OS X on the Mac has support via Quartz Extreme and Core Image technology.
