Microsoft will force PC makers to stop selling machines running Windows XP by the end of this year, despite ongoing compatibility problems with the firm's new Windows Vista OS and continued demand for XP from users.

Demand for XP is particularly strong among small and medium-sized businesses, according to Dell. Since the launch of Windows Vista, the firm has continued to sell some machines with XP pre-installed, and plans to continue doing so throughout the summer.

However, the clock is ticking, and Dell and other PC makers will be obliged to stop selling machines running XP by the end of the year, despite ongoing compatibility and performance issues with Windows Vista.

Dell has decided to continue offering XP on business systems throughout the summer in a feature called Customize With Windows XP, the company said in a recent blog post.

Dell said the move reflects strong demand for XP machines, especially for smaller businesses, which often buy systems in small numbers from OEMs (original equipment manufacturers).

"Dell recognises the needs of small business customers and understands that more time is needed to transition to a new OS [operating system]," said Tom West, director of small business marketing at Dell, on the company's blog. "The plan is to continue offering Windows XP on select Dimension and Inspiron systems until later this summer."

Dell isn't planning to offer XP on consumer systems, saying they prefer the "latest and greatest", a situation that displeased some customers. "Thumbs down for not offering this to home users," wrote one user.

"Many home users - especially gamers - do consider XP the 'greatest' - especially after all the media articles and benchmarks showing very poor gaming performance and compatibility on Vista," wrote another.

At the end of this year, however, Microsoft OEMs' contracts will no longer give them the option of selling XP-powered machines. This is despite problems that have surfaced for consumers as well as businesses, such as games and application incompatibility and driver problems.

Most recently, users complained that Vista's startup, shutdown and application load times are longer than those with Windows XP. Users on Microsoft's Performance & Maintenance forum, who sound pro-Vista for the most part, have expressed anger about a variety of speed issues.

"I have XP and Vista running side-by-side but I twiddle my thumbs waiting for certain apps to load up on the Vista machine while the load is instantaneous on the older XP machine," wrote a user identified as William. "I've tweaked it as best as I could with the info available and I am still very disappointed."

Doubts have also been raised about Vista's security, after it emerged that Vista was affected by recent widespread hacks involving Windows' animated cursors, even though that portion of the code was addressed by an update more than two years ago.

Click here for our review of Windows Vista.