OK, no responses but I was able to recover it myself. I'll share with you what I did to regain control again, maybe it will help someone else!
First I cleaned things up again with CCleaner and CWShredder.
Going through the hijack log again, I checked all unfamiliar programs on the web. I found PSGuard and switpa.exe to be possible malware. I fixed those with HiJack.
After that I ran again through all the described procedures on this forum (smitfraud.reg, hoster, deldomains.inf).
After rebooting in normal mode, I still had no control over my desktop. Then I replaced the wininit.dll in C:\windows\system32 with the wininit.dll from C:\WINDOWS\ServicePackFiles\i386.