Requirements?

Sorry if this is a repeat, but I have not been able to find an answer to this question in my searches on the site.

What will the server hardware requirements be for a gallery site that contains approximately 50,000 images, with a max of 20 users accessing it at once? This would be for internal network use only, running on windows server 2003.

How much resources will Gallery use in this situation? I am trying to determine if I should purchase a new server or if one of my existing servers could handle it.