To really answer ... there are 3 quad core high end gamer machines in the house , one is a dedicated media server, and an Xp single core laptop.
Up until a month ago there were 2 quads, and two old dual cores on vista. I sold the machine I ran E&B on originly, BUT i run it on a laptop I enherited back from somone. ( an aspire 9400 with 2 g's of ram, so about the same as a good desktop would have been in the E&B days ) , I doubt I will upgrade it, Microsoft says it will run Windows 7 but it's almost as cheap for me to buy a new laptop and I play Startrek online so I think I see one in the not too distant future.
We just got rid of the last of the vista virus in the house and upgraded to windows 7. I oddly only hated vista for being slow and a Memory pig. We somehow managed to avoid all the problems with it everyone had. Yeha oddly Xp was more drama here ... I will never know why ...