Silk is not a theme, it's a prefence pane to control fonts. You can use it with any theme.

Go to the Silk pref pane and to the third tab, and set the 'Original Font' to Lucida Grande and the 'Replace With Font' to whatever font you'd like to see. Don't start checking those two little boxes below or some apps won't work.... expecially Chimera.
Then you have to restart the each app to see the font in the menubar and the app, or just restart the whole computer. And I think you have to have Unsanity's .ape thing installed too, but probably most people that are messing around with this already do.