One of the new features in flash player 10 is the ability to read data from the system clipboard.
You can read from the clipboard using Clipboard.generalClipboard.getData(), and write to it using Clipboard.generalClipboard.setData().
In the previous player, you could set clipboard content using System.setClipboard, and as far as I know, this still works. Note, however that now you can only read from the clipbord from within a handler for Event.PASTE, and you can only write to the clipboard from within an Event.COPY event handler. Now I know what you're thinking - "dispatchEvent( new Event(Event.COPY) );" right?