Unable to Install Citrix XenDesktop VDA 2.x-5.6 on physical machines with Windows 7 with WDDM Drivers
Here is a good reason why you should upgrade to Citrix XenDesktop Feature Pack 1
Users are unable to install XenDesktop 5.6 and lower versions on physical Windows 7 computers with WDDM display drivers.
XenDesktop 5.6 and lower versions do not support the use of the VDA on an operating system with the WDDM display driver.
Upgrade to XenDesktop 5.6 Feature Pack 1 and use the Remote PC feature.