Just before you buy a new PC

Windows 7 is on the way. It'll be launched in October, and PCs bought between now and then will qualify for a free (or very cheap) upgrade.

Windows 7 promises to be be faster to boot up than Vista, and with fewer of Vista's annoying habits - but with the extra security that makes Vista a bit less prone to viruses than XP. If you're buying a new PC - check whether it has the Windows 7 upgrade option attached.