gototags.com has both a .NET NFC SDK and a Windows NFC application. You can buy the SDK and starter kit at buynfctags.com. Windows 8 has built in support for NFC, although it doesn't cover the full stack of what you will likely need for an application.
A related note, if you are looking for a Windows-based SDK there is a big difference between the PC/SC (smart card) based SDKs and the native SDKs. Using PC/SC with NFC is a bit of a hack; it works for the basic tag reading and writing, but since you do not have direct access to the NFC chip you will be unable to do any of the more advanced NFC functions such as P2P. Also the PC/SC stack is useless if you need to do high-speed reading or encoding of NFC tags.
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this is a commercial package.
I had found this link,but the link does not work anymore.
Plz help me to find this SDK. I really need this.