The first thing you may notice differently about the Radeon 9800XT is the new heatsink design. This new heatsink design is very massive, but unlike one of ATi's competitors, this heatsink doesn't take up a PCI slot. The heatsink is made of copper and it provides better overall cooling versus the old aluminum heatsinks we've seen in the past. You may also notice that the ram is covered by this massive heatsink along with the core of the 9800 XT.
This is to insure that the ram remains cool during intensive gaming and during the dynamic overclocking that is built in to this card and the Catalyst drivers. We'll talk more about that later :) For those of you that are wondering if this fan is loud or not don't worry, it's actually very quiet. I could detect a slight sound difference between the 9800 XT and the fan on my Radeon 9700 AIW.
On the back of the 9800 XT, you'll find a thin copper heat plate that helps to support the large copper heatsink and also to increase the surface area. This support is necessary since the heatsink weighs so much.
This is a close-up picture of the heatsink. You can see the heatsink is made up of several hollow air channels. I expect these channels help to dissipate the heat better.
With the 9800 XT and the 9700 AIW side-by-side you can see that the 9800 XT is slightly larger in width and also in height. This picture also shows how much larger the heatsink is on the 9800 XT than on the 9700 AIW.