Re: Installing issue
ahh I see your problem ,while i checked your site.
1.You have wordpress mu installed in a subdirectory wpmu
2.But you have installed wordpress mu to use subdomain style address ,which will not work.
Workaround
1.Install wordpress mu in wpmu(subdirectory as it is now) but at the time of installation select “Sub- directories” and go ahead, your wpmu will work correctly and you will have blogs with address as
idotter.ch/wpmu/blog_address
Or
2.Install wpmu in the root domain with subdomain style,enable wildcard subdomain and you will have blogs like blog.yoursite.com working.
Hope it helps.