Hi,
This topic was covered on these forums multiple times already. Also, please refer to the Implementation Guide to find the hardware requirements:
http://www.microsoft.com/downloads/details.aspx?FamilyID=1ceb5e01-de9f-48c0-8ce2-51633ebf4714&displaylang=en.
If I could suggest anything, I would recommed splitting the web server and the database server on two machines (they may be virtual). Each of them should have 8 GB RAM, QuadCore processor (e.g. 3Ghz). The disk requirements differ and are dependent on what data do you want to store in your CRM (big attachments? only objects? documents?)
I hope that helps,
Kuba
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Kuba Skałbania, Netwise