As far I know (I stopped bothering with video cards back when 512 megs was top line and x16 was all the rage and SLi wasn’t a “stock” feature) You can not plug in anything that isn’t supported, just like ram. I know that my 8x card would not fit my 16x slot, and of course vis-versa. If you are wondering, try to figure out what video card you have and check their website, if nothing else that will tell you what type of card you have and can use. Don’t quote me as law, as I am “out of the loop” with technology like that. But I am pretty sure they (the video card companies) wouldn’t switch anything up, even with Vista.