Below this guide to use this themes :
Un-compress Tish-Clearlooks-AquaStyle and put in your /home/your_userame/.themes/ directory
Right Click onto the top panel, and chose properties. In Panel Properties, choose advanced tab and select the background image then browse trough Tish-Clearlooks-AquaStyle directory and find panelAtas.png.
Change your button layout from GConf editor and go to /apps/metacity/general, right click the button layout and edit the value for menu to look like this : close,minimize,maximize:menu
Replace icon with OSX icons. Get OSX icons from here
The other alternative instead of editing looks from the gconf editor, you can uncompress gconf.tar.bz and replace your /usr/share/pixmaps/gconf-editor directory.
Look other gnome lovers say about this themes ?? You can go here.
Download this themes : Tish-Clearlooks-AquaStyle Themes (134 kb)
I hope you enjoy using this themes :-)