> Is it possible to apply file size restrictions.  For 
> example: download all gifs over 1kb, or all jpgs under 20k?
Try filters like the following to exclude all gif files smaller than 1KB and
all jpg files over 20KB:

+*.gif -*.gif*[<1] -*.jpg +*.jpg*[<20]

Also, have a look at Fred Cohen's HTTrack guide, under the "Filters" heading:
<http://www.httrack.com/HelpHtml/fcguide.html>