|First, I would use VirtualBox as your VM Software (it's free and has lots of options to make the OS run better).|
Second, your setup could be a problem. Windows Server 2008 needs activation. Installing it in a Virtual Machine will take up one of the licenses for the software. You can find out how many licenses you have usually listed somewhere on the box. If it is 1 license, you won't be able to install it again after you install it in a VM. If it is, say, a 5 license, you'd be okay installing it in a VM. But if it is 1 license, and you plan to use it on a real machine, you can't install it in a VM.
But I have another solution for you. It is called the TechNet Labs. It lets you try out an Operating System in your Web Browser. The downside is that it must be done in Internet Explorer, and you can only use the Operating System for 90 Minutes. To get to these labs, open this link in Internet Explorer:
You will find labs for Windows Server 2008 on the page.
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