VMWare servers running Citrix 4.5 Virtual Server

We have 3 Citrix 4.5 XenAPP servers running on ESX 3.01. servers providing desktops to users. The ESX servers have 2 Quad Core 1.862 GHz processors with 16 GB of RAM. There are other virtual servers running on the ESX servers, but the Citrix servers use 1 CPU with 3 GB of RAM assigned to it. Our users are access the Citrix servers from Neoware thin clients. We are getting reports from staff that the servers (newly built and not overly used - less than 10 users per server) are slow. We notice that there are times when IEXPLORE.EXE and/or OUTLOOK.EXE tie up CPU resources so that the server is at 100%. We have followed best practices and setup the Citrix servers with 1 CPU, disabled the COM ports. Still having problems. Today, I changed the setting to make sure the virtual servers have scheduling affinity so that they run on a specific processor. Has anyone seen such problems and if so, what did you do to resolve???