It makes me said when I see designers treating tracking as kerning. For the most part, Typography is a lost art on the web, even though it should be treated as a first class citizen. The good news is tracking, unlike kerning, is something we can easily translate into the CSS attribute letter-spacing.
For the uninitiated, tracking is the adjustment of the spacing of characters throughout an entire word. When used for evil it can severly impact the legibility of the type. So use it for good people.
letter-spacing = tracking / 1000
0.2 = 200 / 1000
This is where you can find the tracking value in the Photoshop character dialogue.