Hey,
I unzipped and copied Arctic manually into the tpl folder.
When I enter the url, out comes a huge bunch of code starting with:
a.interwiki{background:transparent url(/dokuwikitest/dokuwiki/lib/images/interwiki.png)
Actually this lost a bit of urgency; I just installed Monobook the same way, switched themes and it works. (!?)
If you still can help me with this issue - which might be of importance at some point in the future, I don't know? - that would be nice anyway!