Probably the cheapest route to getting Windows 8

If you are inclined to upgarade, read carefully.
Microsoft today opened its virtual store and began selling upgrades to Windows 8 Pro for $39.99, making good on a promise made last summer.
The upgrade, which must be downloaded and installed via a utility called "Windows 8 Upgrade Assistant," can be applied to Windows XP-, Vista-, and Windows 7-powered systems.
Microsoft announced the upgrade in July, a bit more than a month after it issued the last of three public previews, but before it wrapped up its work on the new OS.
The upgrade does the most thorough job when migrating a machine from Windows 7, which is the only edition that conducts a "full" upgrade, the label for an upgrade that brings along everything, including data files, user accounts, Windows settings and installed applications.
Windows XP-to-Windows 8 upgrades are the least comprehensive, allowing customers to move only personal files; Vista transfers both Windows settings and personal files to Windows 8.
Although the $39.99 buys only the upgrade's 2GB digital download, users can optionally request a DVD for an additional $14.99. The combination is about $15 cheaper than the $69.99 DVD-in-a-box that Microsoft and retailers, including Best Buy, Wal-Mart and Amazon, are now selling.