Welcome to the forums - there are a couple of ways to do this - the issue with changing the ESX 2.5 to OVF issue is I am not sure that there is any way to do that - I do not know if you have looked at upgrading your existing 2.5 server or not - if there are issues in doing this I would recommend using VMware converter - also I do not know if you have seen this PDF or not covering how to upgrade from ESX 2.5 to VI-3 -
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