I think the character set issue is the result of the .net install. And I don't think the problem is because of the Windows 2003 US edition.
But I could be wrong.
Can you remove the aspnet_isapi.dll ISAPI extension from the website instance you have the blog in and try it?
Here is my reasoning:
The blog application itself sends the correct charset header. This means something else is conflicting with this. I see no conflicting headers sent to the client. But I do see the X-Powered-By: ASP.NET header sent for all files (including images). I believe this means everything served from the server is running through the asp.net extension (which wouldn't surprise me, since it has some nifty webside authentication and file security tricks).
Now, I haven't played with IIS 6 at all, and I have only played with .net a little, so I can't help you on the configuration of the server. I think you may be able to add a web.config to your web directory to configure asp.net for that webserver instance, or you can fiddle with machine.config file which is located in Windows\Microsoft.Net\Framework\xxx\config directory (where xxx is 1.0.3705 for version 1.0 of the Framework, or 1.1.4322 for version 1.1). Look for the globalization section.
A good resource about asp.net configurations is msdn magazine. A specific article for you would be:
http://msdn.microsoft.com/msdnmag/issue ... ASPColumn/
But that has exhuasted my knownledge.