Hi Tack,
Yes, you must secured those important accounts, you should not memorize it , you have be assure what password did you use. Because windows 2008 is totally high secured, maybe you missed something.
Anyway, you may use this reference about Microsoft Windows 2008 Hyper-V RTM Installation & Configuraiton step by step. This will help some guidelines and tips..
Thanks.
---Always here to help you..