This addon is for Mists of Pandaria classic, for retail check this addon: Talent Tree Viewer (calculator)
Usage is simple: click the minimap button, or type /ctv, /tc or /talentviewer in chat to open the talent frame
Use the dropdown to pick between any class and view their talents, you can also scroll over the dropdown to switch between classes
The talent frame looks like the default blizzard talent frame
You cannot change talents, or view what talents you have selected, but you can link talents to chat or to macros; and of course, you can view the tooltips
This only works in classic, from MoP onward!
You can download BlizzMove to make the Talent UI movable and resizable