Probably the most dramatic is a discount for families running multiple computers at home. From Jan. 30 to June 30, North American customers who purchase an upgrade or full retail copy of Windows Vista Ultimate will be able to buy one or two additional copies of Windows Vista Home Premium for use on other PCs for US$49.99 each.

Windows Vista Home Premium lists for $239 for a full retail version and $159 for an upgrade from Windows XP or 2000.

But to get the discounted price, users will have to lay out a tidy sum: $399 for a full version of Windows Vista Ultimate or $259 for the upgrade from Windows XP or 2000.

While the discount is targeted at families, small businesses can take advantage of it, too, a Microsoft spokeswoman said.

However, customers who only own an OEM version of Windows Vista Ultimate -- that is, one that was preinstalled when they bought a new PC -- are not eligible for the discount, the spokeswoman said.