http://maps.eq2interface.com/index.php?ID=download
Under that auto-updater is a manual update. Just download the zip file and extract it to your custom UI folder.
As for that 404 error, i'm not sure what to suggest. If you can view the XML in internet explorer then you should be able to view it in the auto-updater. I'll have a think and maybe taco-man has a suggestion.