Citrix (CTXS) is different than VMWare. A Citrix console MAY LOOK like a VMWare virtual server but it is not. Citrix is terminal services which is very different in construction, concept, and application. Citrix serves a different function in an enterprise environment than VMWare. Not the same.
Um FA7, Citrix owns XenSource the only other true hypervisor on the market. It is exactly the same thing that VMW sells. It just isn't as mature. SWSoft has a product as well. So does Virtual Iron. MSFT is supposed to be coming out with one this year as part of Windows 2008, but it won't be here for a while. Citrix also has Presentation Server as you have mentioned. Couple Presentation Server with XenServer and then add their WAN and LAN optimization tools and CTXS has a pretty mean offering. Granted VMW is more mature in the Server Virtualization Offering. However, CTXS is Application Virtualization with the ability to virtualize everything from the server on up.