> i tried to use the filesize-filter (like in -*.jpg +.*jpg*
> [> 20]) but it does not seem to work, smaller files are 
> still downloaded.

-*.jpg*[<20]
is also possible.

Remember that httrack will issue the request anyway, 
possibly causing to create an (empty) file, because the 
file size if given in the server response.
And this will not work properlky if the server does not 
give any valid size, too.