> suppose i have a partial copy of a site on my hd done via
> httrack. suppose i have some other files from that 
websites
> downloaded with some other program. now suppose i want to
> integrate those files into the project's dir, so the next
> time i run httrack i will not fetch those files as they 
are
> already  exisiting locally.

There are two points you have to check:
- the files location must match exactly the location they(d 
have if they were downloaded by httrack
- the files must be authorized (use "Set Options"/"Scan 
rules" is necessary)

And then run "Continue an interrupted mirror" (--continue). 
This should work.