Looks the same to me with Cleartype on.
I was using Cleartype for sure - it seemed as though the fonts were too thin or something. Definitely worse than Vista. It might have been because my contrast is so high and the red/green/blue sub-pixel antialiasing on XP's cleartype is less subtle.
Edit: I think this is it - on my XP computer I can distinctly see the red pixels on the left of black text and blue pixels on the right. On Vista it's much less apparent, although still there. This seems to result in sharper, darker text. XP's method is probably better suited to lower resolution, lower contrast screens.