Virtual Drumline comes with the Kontakt Player software developed by Native Instruments who have stated:

Native Instruments has conducted compatibility tests with Windows 7 that have shown current NI products to work without any specific issues under this operating system. In general, users involved in professional audio production or live performance should be cautious about upgrading to Windows 7 until compatibility with third-party audio software and hardware has been widely confirmed by the relevant manufacturers.

 

To summarize, NI software (including VDL) should work with Windows 7, but you should be sure to check that the audio hardware (i.e. soundcard) and any other software you intend to use in conjunction with VDL have drivers that are compatible with Windows 7. For more information, visit the Windows Compatibility of Native Instruments Hardware.