Why was I not informed of this Thunderbolt, of which you speak?
Probably. Mine at home says no hardware found for Thunderbolt because my iMac does not have a Thunderbolt port. It might automagically install the driver if you plug a Thunderbolt device into it. Have you looked on the back to see if you have a Thunderbolt port?
I use one of these USB devices to hook up my third monitor to my iMachttp://plugable.com/products/uga-2k-a/get the drivers here as the box does not have the latesthttp://www.displaylink.com/support/mac_downloads.phpworks fine with Lion. Res is not top end but it drives a 22 inch just fine.