afaik, this is not available via the VI/vSphere API, if you have VMware Tools installed, you can get the following networking information from a VM: http://www.vmware.com/support/developer/vc-sdk/visdk400pubs/ReferenceGuide/index.html
You may want to take a look at VMware VIX API which can do this but the current 1.6.2 version does not support vSphere, just VI 3.5
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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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