As I suspected, this SDK is obsolete and is no longer available.
Sounds like it has not been available for years.
Thanks Lance Atencio, for your information.
To enable network booting in legacy environment still most of platforms are using PXE (PXE-BC & PXE-UNDI) Expansion ROMs. So whenever new platforms come up, it has its Pxe Option Rom to add network boot functionality. So still most of places it(PXE SDK) is being used to devlope the same. Kindly correct me if i'm wrong.
Thanks again for your time
Jram