What will it take for your PC to run the latest version of Windows? No matter what software or OS you choose to run, your hardware has to be up to snuff in the first place. The PC you own now may not even be able to install this "next-gen" Microsoft OS. Want to switch from 98, 2000 or XP? You may want to make an upgrade plan now. Some of the requirements are pretty steep. Though I can testify to it running decently on older hardware, this eweek article goes into detail on the minimum and recommended specifications.
Among other things, a DX9 capable video card and 128mb of RAM is required. Though 128 may not seem like much, keep in mind that XP has a minimum requirement of 64mb RAM. Anyone trying to run XP with 64mb will let you know how awful slow it is. Take a gander if you are planning to upgrade.