Windows 7 is supposed to be released next year, but I wouldn't be surprised if it's delayed until 2010. I've used the Win7 betas quite a bit, and if the final product is like them, I'd say that the future of Windows is looking good. It essentially has all of Vista's benefits (improved audio architecture, DX10, GPU-accelerated interface, some other minor things) with a lower memory footprint and a few new ideas tossed in as well. The new taskbar (I think it's called "Superbar") is kind of neat but shall require some getting used to.
XP's support lifecycle isn't ending until after Windows 7 is released, so it's quite safe to stick with it, and it gets my recommendation.