[arnova]

Sounds like a problem with the repository (mirror) you are using. The package libsdl-.... really exists in ubuntu/main (both hardy & intrepid on x86). You could first try an "aptitude update", if it fails try stuffing another mirror in your /etc/apt/sources.list

[Macro]

hmm...I tried that out, without success.

I tried the icelandic (currently working here), German, and Main-Server for the packages

[arnova]

Is it 32 or 64bit you're using?

[Macro]

32

I guess I have to check my packages, since you said that this libs are in the official repositories the problem relies probably on my side.