Hey Crabby,
We do make templates that accomodate the 800x600 crowd. If you look in our template gallery look for templates that only use a colored background and maybe a header and footer image. This kind of template works best for those particularly concerned with the width of their display. Otherwise a vast majority of our templates are built with the consideration to the same 800x600 crowd, meaning if the seller uses a single image across at say 400x300 and the text for the description below that image, the template should display properly without having to scroll left and right to see the entire listing. Of course you can see the problem one might have when they pair even two images across at that same size. The image space alone comes to 800 pixels and when a listing is inserted into eBay it is given something like 98% of the screen so that would instantly cause a scroll bar to appear, even without using a template of any kind.
Secondly, I would like to cast a shadow of doubt on this statistic that I see way to many people using, about MOST eBay buyers using a screen resolution of 800x600. I tried to stay informed about these issues for they are important to me and my company. There are plenty of websites out there that gather data on screen resolutions of users and by and large most people have their monitors set to a high resolution.