Ultimately, the great majority of home computer owners will have a Vista system because almost all new PCs are going to come with it already installed. Microsoft has too great a hold on the market for its dominance to be going away. Nonetheless, there are viable alternatives and they are discussed here.
Windows XP as an alternative to Vista
In many ways, Windows XP is going to be the strongest rival for Vista for some time. If you have an existing Windows XP system that is meeting your needs, there is no compelling reason to rush to Vista. As discussed on another page, there are system requirements that may mean that your present hardware is inadequate for Vista. Windows XP SP2 will continue to be supported by Microsoft for a number of years. Until April, 2009, all versions of Windows XP SP2 will receive free security patches as well as non-security related updates. From April, 2009- April, 2014, all versions will receive security related patches only. Many will conclude that they will switch to Vista only when they get a new machine.
Even those who buy new systems will have the option to choose Windows XP for some time to come. Microsoft has said that Windows XP Professional will still be available to major vendors until the end of June, 2008, Small system builders will be able to install XP until the end of January, 2009. Not all PC vendors will be giving the option of XP but copies of the XP disc are going to be around for quite a while.
Apple Mac as an alternative
The new Intel-based family of Mac computers is an attractive alternative for the home computer user. Many of the features that are new on Vista are already present on the Mac. There are numerous discussions on the Web comparing the Mac with Vista. For a reasoned example see Scot Finnie's discussion of why he switched to a Mac. Another article about switching is by a long-time Microsoft fan who is disappointed by Vista .One drawback to switching to a Mac is that software has to be replaced. Also, not everything has a Mac version. However, there are Windows emulators that allow for a variety of Windows software to be run. Also Windows XP itself can be run on a Mac either in a dual-boot setup (Bootcamp) or as a virtualized system. The best known of the virtual machine software is Parallels.
Linux as an alternative
Linux comes in a variety of distributions and some of these are aimed at the personal computer user. However, in my opinion, there are still issues about usability. Linux is a fine system for those who like to tinker but the typical home PC user is usually not interested in the additional steps that are required to run Linux. There are also some limitations on software and driver availability. In spite of its virtues and its large presence in the server market, Linux does not yet look like a practical alternative for the average, non-technical home user who wants an appliance.
Update: It begins to look like a number of computer manufacturers will be selling low-end systems with Linux preinstalled. These system are primarily in the small notebook category.