What they've done at the driver level is found a way to split off some workload that is normally handled in a single thread, into two thread if a Dual-core is present. It is this kind of work that, as it matures at the developer end, that will begin to take advantage of Dual-core.
However, the gains in performance will not justify the additional AMD cost differential for most gamers... the X2 4800+ (dual core, San Diego 1MBx2, 2.4GHz) is $803 while the single core 4000 (San Diego 1MB, 2.4GHz) is $334, or the dual core is 2.35 times more expensive for an average 8% gain. Put another way, in reference to the 4000+, for a gamer's 8% gain, you spend $470. Most people can recover 8% for free by simply partitioning their hard drive optimally and moving the swapfile. And most can recover from 5% to 20% by removing unnecessary processes and unnecessary services when gaming... for free. And $470 can get an upgrade to a top of the line video card with leftover.
But in a few months, the dual-core will be more widely supported by developers, and its power (it does have strong gaming potential... the X4 will probably be a true single-core CPU killer when coupled to a good OS in a couple years) will begin to emerge. But by then better and faster CPUs will be out (maybe even from Intel), taking the place of the 4800+ for the same money.
By applying the savings of X2 for an equal single core in today's best games, you can get speed and quality with a top video card, the fastest hard drive (e.g., Maxtor DM 10 w/16MB, and 2GB of Fast RAM and the best motherboard:
nVidia 5xxx, PixelShaders to "Low" in Age of Empires III: deactivates shadows.
nVidia 5xxx, "Medium" setting: allows simple shadows.
nVidia 6xxx, On the "High" setting: PixelShader 2 and 2.0b, shadows are reflected in the waves.
nVidia 6xxx & 7xxx & ATI X1x00, "Very-High" (PixelShader 3) shows all details and additionally makes the water transparent.
When you play the games side by side with such hardware differential, you will be blown away. You will not be able to feel or sense the difference in X2 and single core, even if price is no object, in today games and through the end of next year at the earliest (sources: THG and MS and Intel, developer evangelism).
EDIT: Typo & link.
[This message has been edited by Wartrain (edited 12-12-2005 @ 11:41 AM).]