> I have downloaded entire site- and wanted to update the 
> mirror. Unfortunately the server limits transfers- so I 
> received error message. WinHTTrack has overwriten headers 
> of all jpeg and mpg files in such a way, that I can no 
> longer use them. Each header contained 
information :copied 
> with winhttrack and 'the file was temporarily moved'.

I suspect that the files were giving redirects (302) to 
error pages, isn't it?
There is no much things to do, except setting reasonnable 
transfer rate limits (like 10KB/s) and simultaneous 
connections limits (1 or 2 sockets simultaneously)

> Seems here should be introduced not only file-size check- 
> but also checksum

Checksuming is impossible with http (there are no 
such "built-in" features), even if it can be acheived with 
etag (but very few servers are using it)