I beleive that is known as a Dual-Head card. Dual link is a way to get more bandwidth for higher resolutions and refresh rates. That's abotu all I know about it.
Dual link refers to a single DVI port that offers double the bandwidth of a single link DVI port. You can, in other words, have two dual-link ports on one card (as the X1900 does for instance). You'll notice that a DVI socket on a vid card has tons of little holes - on a single link port some of those are basically dead or not wired up. On a dual-link port, all the holes are enabled providing more bandwidth and enabling higher reoslutions (resolutions above 1,920 x 1,200). Likewise, you'll need a dual-link cable with a complete set of pins. A single link cable has fewer pins - the pins required for the "second" link are not included.
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