Windows 7

Windows 7 runs smoothly on a Celeron PC with 512megs of ram, and will perform even better with readyboost. There are some driver issues on certain laptops (as can be expected of an operating system that hasn't been released yet), but otherwise, by far the best operating system Microsoft has ever built and is a true successor to XP. My recommendation is, install it on your PC, or if you have a laptop, look in online forums first to see if there are any huge driver issues for your particular model. MS has already stopped downloads from their website, but I'm sure you can find build 7100 or even 7600 online, and you can get a trial serial number on the MS website until Oct, which lasts until July of 2010. So whacha waiting for, folks?!