> I'd like to take pages that have an address like
> showthreads.php?v1=bar&v2=foo
> 
> and convert them into files like
> showthreads.html?v1=bar&v2=foo.html
> 
> Is this possible? 
the first the server sets to environment variable v1 and v2 and runs the php
script. The second is an invalid file name. so No.

you can have the files named showthreads_v1-bar_v2-foo.html and the like. 
User-defined structure -
<http://httrack.kauler.com/help/User-defined_structure>

> I also need to limit all the
> requests so that sites like photobucket aren't
> cached in my mirror of the forum. 
The default is to stay on the original site.