Not aware of a script, you could do a search on the forums to confirm.
You would take a look at UpgradeTools_Task() http://www.vmware.com/support/developer/vc-sdk/visdk400pubs/ReferenceGuide/vim.VirtualMachine.html#u...
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William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at:
VMware Code Central - Scripts/Sample code for Developers and Administrators
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