How can you get the server to tell you how much time is left on a Windows Server 2008 evaluation installation?
Run the Slmgr.vbs script that is in the System32 folder. Use the -dli switch to run this script:
slmgr.vbs -dli
The command displays the number of days that are left in the current 60-day evaluation period.
Source: Microsoft Support article 948472 – How to extend the Windows Server 2008 evaluation period
Check more discussion of this question.