ISVs can now receive a special Hyper-V designation to support the Certified On or Works-With certifications for Windows Server 2008 applications. The designation lets those considering your software that it has passed compliance testing for Windows Server 2008 Hyper-V.
Basically to receive the "Certified for" designation, an application needs to pass all the test cases in a Windows Server 2008 virtual machine on a Windows Server 2008 Hyper-V, and four additional test cases that are documented in Chapter 6 of the “Certified for” test specifications and framework.
For "Works with" designation is – the ISV just runs the tool against the application in a Windows Server 2008 virtual machine on a Windows Server 2008 Hyper-V.
The “Works with” test fee will be waived for the first 150 passing applications through the end of FY09.
For more information, see Windows Server Certification. You can update your Windows Server 2008 to include the Hyper-V role from Update for Windows Server 2008 x64 Edition (KB950050).