> if WinHTTrack downloads a file from 
> <http://www.bla.com/path/> it stores it with the filename 
> index.html (because the remote file has no 'real' 
filename).
> How is this file stored in the cache (i.e. new ZIP 
format)?
As regular URL, that is:
<http://www.bla.com/path/>

See <http://www.httrack.com/html/cache.html> for more info

> The reason, why I'm asking is, that I can't see it with 
my 
> ZIP-Tools

Many ZIP apps have problems with this naming system -but 
libraries should access it without problems.