Virtualisation vendor VMware has accused Microsoft of abusing its market dominance to gain traction in the virtualisation market. 

A white paper published on VMware's website on Friday made several allegations of predatory practices by Microsoft. 

VMware is currently the largest vendor of virtualisation software. The EMC subsidiary competes with Microsoft Virtual Server and the open source XenSource technology.

The VMware paper denounced Microsoft for denying support to customers running Microsoft software in a virtual environment, except for companies that have purchased premier support.

Users are then effectively required to replicate an issue on a physical machine to obtain assistance from Microsoft support.

Microsoft is also accused of using its software licensing terms to promote its Microsoft Virtual Server 2005 R2 over competing offerings from VMware.

Microsoft uses licence restrictions to block the use of its virtual hard disk images on non-Microsoft software, for instance, and has disabled software running on a virtual system through its software activation technology.

So-called software appliances provide a bundle of applications and operating system in a single downloadable file and act like a separate physical hard drive inside the virtualisation software.

Windows Vista, for example, does not support Internet Explorer 6, but users looking to run the browser on the new operating system can download a virtual hard disk image that provides them with IE6 running on a stripped down version of XP.

Mike Neil, general manager for virtualisation strategy at Microsoft, denied VMware's claims and stated that the white paper contained "several inaccuracies and misunderstandings of our current licence and usage policies".

"We believe that we are being progressive and fair with our existing licensing and usage policies and creating a level playing field for partners and customers," Neil said in an emailed statement.

"We are deeply committed to providing high-quality technical support to our customers who are utilising virtualisation technology."

Neil invited VMware and its parent company EMC to resolve any issues and misunderstandings.

"We are committed to continuing to collaborate with VMware as we have been doing on regular basis."