> I am trying to mirror a dynamic mod_perl site of mine.  My
> site does not use any file name extensions (except for

Not at all? Couldn't you use something like .cgi?
> graphics).  When I mirror with HTTrack, the software puts 
a
> .txt extension on despite the content-type headers and the
> contents of the file.

Then, the server must repond with text/text
Activate the extended debug mode (option -%H) and look in 
hts-ioinfo.txt : the server may not respond correctly to 
HEAD requests?
Try also 3.23-b10 release, which may be better in handling 
extensions