A more detailed Safari tutorial can be found here

1. Install

First, Please install SIMBL.

2. Download

GreaseKit-1.5.dmg (2008-03-22)

Please copy "GreaseKit" bundle from the downloaded Disk Image.

And paste the copy in the

Relaunch your Safari.

If the installation is successful, you'll see "GreaseKit" on the menubar!