Jon Pugh saw the need to extend the capabilities of AppleScript back in the days before the Scriptable Finder became available. He has released a package of "Free for noncommercial use" Scripting Additions known as Jon's Commands. The extended commands include:
clipboard info - get a list of data on the clipboard
set the clipboard to - put data on the clipboard
the clipboard - get data from the clipboard
This particular set of commands is so popular that Jon separated the clipboard extensions into a stand alone Scripting Addition called clipboard. This scripting addition can be found on the internet.
Scripting the Finder in Mac OS 8.5
Beginning with Mac OS 8.5 it is possible to manipulate data in the Clipboard with the Finder.
The scripting addition file called "Standard Additions" that's part of Mac OS 8.5 has commands for setting the contents of the clipboard, getting the contents of the clipboard and getting information about the contents of the clipboard.
Examples of how to write AppleScripts that do this are available in Mac OS 8.5's AppleScript help under the topic: "Using the clipboard."