For those trying out this new product from Microsoft , heres an article from the software giants themselves showing how to extend the evaluation period to 240 days for this product.
Evaluating Windows Server 2008 software does not require product activation. Any edition of Windows Server 2008 may be installed without activation, and it may be evaluated for 60 days. Additionally, the 60-day evaluation period may be reset (re-armed) three times. This action extends the original 60-day evaluation period by up to 180 days for a total possible evaluation time of 240 days.