Yong,
The only way to currently access a LabVIEW VI from VB.NET would be to create a DLL from the VI and then call that DLL from your VB.NET application. You can not embed the VI directly into your application.
Here is a document from the NI Developer Zone that describes both the creation process for DLL's and has links to documents that explain how to call the dlls in different development environments including VB.
Building DLLs in LabVIEW 6.xZvezdana S.