Hi,
I think you will need to do some more research on exactly what it is you want to acheive, "Cloud" is a buzz word at the moment and it may not be what you really require.
But building a true private cloud would require more than one ESX server and would also involve things like chargeback etc.
With Cloud you would usually have either:
Infrastructure as a service (IaaS)
Platform as a service (PaaS)
Software as a service (SaaS)
It sounds like you are looking for something like SaaS, to deliver applications to users. Try and do some research on Thinapp and also VMware View. Just to be software agnostic also look at XenApp and MS App-V
Hope this can get you started on getting the information you require.