> Is there any other software around that is focused on 
> the 'form submitting' part of spidering??
You may try to ask on the newsgroups ; this forum is mainly 
focused on httrack -- and I don't know if many people will 
be able to answer.

Anyway, you can improve the method by generating 
the "postfiles" by yourself, and then launching httrack on 
them. But it will require some scripting (linux-style)