I'd guess similar themes to be available to also KDE, not just Xfce. (Xfce also has modern looking themes, but the default is very dated.)
Maybe if you picked the right browser and set up some user style sheets you could get things just right.
Before you accuse me of being a curmudgeon, know that I love the Ribbon as well. :)
The actual OS aside, do you prefer the look of Win2000 over the look of Win8?
I get that Win2000 is minimalistic. But it's not too flat that you can't tell what is what. And I like that. But what I hate about it is the colours. Especially the grey, turquoise, and dark blue. They literally nauseate me sometimes. Do you not find the colours off-putting?
I hate the turquoise. Don't mind the dark blue and grey.