VMware expects 14,000 attendees at its annual user conference in Las Vegas this week, including workers from more than 200 trade-show exhibitors.

That's a 30 percent increase over last year's attendance -- clear evidence of VMware's influence. But VMworld 2008 will also be the focal point for the gathering storm of competition that the virtualisation market leader faces.

Among the companies fighting for users at the conference will be the first serious challengers to VMware's dominance of server virtualisation. That includes Microsoft Corp., which released its Hyper-V virtualisation hypervisor in June, and Citrix Systems, which today plans to announce a new version of the XenServer software that it acquired last year.

VMware has let competitors set up booths at its shows since the first VMworld in 2004, but it still controls the conference agenda. One scheduled presenter, Simon Crosby, Citrix's chief technology officer, said his slides had "to be vetted by the censors" -- a reference to VMware. He added that his talk was "carefully arranged" by VMware to take place in the afternoon on Thursday, the last day of the conference.

Indeed, VMware continues to set the agenda for the entire virtualisation market. Rivals and hardware vendors alike have timed product announcements to coincide with VMworld.

In addition to Citrix's scheduled rollout, Microsoft last Monday said, at a launch event that it would ship a free stand-alone version of Hyper-V and an upgrade of its virtualisation management tool within 30 days.

And on Wednesday, Sun Microsystems -- which will also have a booth at VMworld -- formally announced its first virtualisation offering that supports multiple operating systems.

Also last week, Dell Inc. added two blade servers geared toward virtualisation. And Hewlett-Packard, which announced a set of virtualisation-oriented products two weeks ago, will unveil more offerings today, including a server based on a six-core Xeon processor that Intel announced in conjunction with VMworld.

As competition has picked up, though, VMware has lost its ability to control one important thing: pricing.

In July, VMware made its low-end ESXi hypervisor available free of charge. Then last month, it adopted a new pricing scheme for its Lab Manager tool for developers, lowering the starting price for deployments from about $16,000 to between $2,000 and $4,000.

Users are taking advantage of the new era of free hypervisors and reduced pricing for the software layered on top of them.

These are dangerous times for VMware -- a fact that it acknowledged in July, when it ousted CEO Diane Greene -- a collegial, research-oriented leader who was one of its co-founders ? and replaced her with onetime Microsoft executive Paul Maritz. In his first press conference, Maritz touted his inside knowledge of Microsoft's battle tactics and said he knew how to defeat the software giant.

Maritz announced the ESXi giveaway during that same conference call. His appointment and the subsequent pricing moves by both VMware and Microsoft suggest that the competition for virtualisation users may mirror the blunt-force browser wars between Microsoft and Netscape in the late 1990s.

For now, VMware's technology still gives it an edge. Rachel Chalmers, an analyst at The 451 Group, said that tools such as VMotion, which lets users do live migrations of virtual machines from one physical server to another, put VMware "in a very strong position."

But rival products are improving. For instance, Citrix's new XenServer 5.0 includes the ability to boot and run a virtual machine on a bare-metal server without a hypervisor, potentially eliminating the performance concerns that often keep IT managers from running mission-critical applications in virtualized environments.

XenServer 5.0 can also manage virtual servers based on Hyper-V and VMware's software. Microsoft's new virtualisation management tool will be able to control VMware-based servers as well, and Microsoft last week demoed a live-migration feature that's scheduled to be included in the next release of Hyper-V.

Most vendors won't allow direct rivals to exhibit at their own conferences. But Karthik Rau, vice president of marketing at VMware, said the company wants VMworld attendees to get a comprehensive view of virtualisation technology. VMware is confident that users will continue to choose its products, Rau added.