Absolute blog URI is a problem

I just started using WP 1.5.1.

An option exists to fix the blog URI. My blog resides on a machine that I must access with different names, depending on where I am connected: from my room I’ve an internal name for the machine; from the Internet there is a dyndns. If I set the blog URI to fit the first, the access from the second does not work. If I set the blog URI to the second, the access from the first does not work. Should WP not gather the blog address from the URL used to access it?

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