One of the new things in Numbers '09 is AppleScript support. As an example of what's possible -- and the kind of code you'll need to use to get the current sheet and selected cells -- AppleScript guru Sal Soghoian sent in the following example. This code takes the selected cells in a Numbers table and converts them into a bulleted slide in Keynote with the selected values.
To use this, save it out of Script Editor as a script to your user's Library » Scripts » Applications » Numbers folder -- you may have to create some of the folders at/below the Scripts folder. Then within Numbers, select the range you wish to move to Keynote, and then use the Scripts menu to select and run your new script.Mac OS X Hints
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