Whether for the limited-time savings or an eager need to ditch Vista, preordering of Windows 7 has been immensely popular at certain online retailers. Amazon.com in particular has handled quite a number of orders placed for the operating system, with the majority of people buying the $49 upgrade version of Windows 7 Home Premium. As it stands, the package is ranked as number one at the retailer’s electronics products section, beating all other software and electronic gadgets on the site.

Microsoft’s pre-retail success with Windows 7 is not exclusive to the US either, with several reports around the web suggesting that demand has exceeded the company’s expected supply in Japan. As far as ad campaigns go, Microsoft hasn’t played up Windows 7 nearly as much as they did Vista, so why the demand? – Especially after such a short time since Vista’s release. Whatever each individual’s reason for upgrading is, it seems Windows 7 is off to a good start but can it keep it?  That is the question people want find out.

From Friday through July 11, consumers in the U.S. will be able to buy an upgrade copy of Windows 7 Home premium for $49 or Windows 7 Professional for $99. That offer is good for both XP and Windows Vista PCs, regardless of whether someone has been trying out the pre-release version of the operating system. That matches the details in a memo from Best Buy that leaked earlier this month.

When boxed copies of Windows 7 go on sale on October 22, Microsoft plans to charge $119 for Home Premium, $199 for Professional and $219 for Ultimate. The Home Premium upgrade is down $40 from the product’s original price, although the Vista product had already gotten a price cut along the way. The Professional and Ultimate versions are priced similar to where Microsoft was with Vista. The upgrade prices apply to those moving from a previous version of Windows to Windows 7, but only those from Windows Vista will be able to upgrade without doing a clean installation of the product.

The full versions of Windows 7–the editions for those without a copy of Windows–will be priced at $199 for Home Premium, $299 for Professional and $319 for Ultimate. The Ultimate and Professional editions are again on par with their Vista counterparts, while Home Premium is down from the $239 that Microsoft had charged with Vista. Microsoft also plans to offer the operating system in an easier-to-open box.

Of course, even at the preorder price, Microsoft still finds itself undercut by Apple, which has said it will only charge $29 for Leopard users moving to Snow Leopard (those on older versions of the Mac OS will have to buy a full-boxed copy combining Leopard and Snow Leopard).