You should be able to determine the IIS version number from the following registry value: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\InetStp\VersionString
This shows "Version 6.0" on my local machine.
(You can find details on how to open regedit to view this from http://www.wikihow.com/Open-Regedit)
reg.exe query HKLM\SOFTWARE\Microsoft\InetStp /v VersionString