> I'd like to ask whether it is possible rename
> (-N option) only html files,
> but to keep names of other files (images etc.)

No - you will have to patch the htsname.c routine, or 
write an C handler using the httrack library.

> Yes, and another question - I really _need_ download
> files without extension (no '.' (dot) in name) linked
> from pages. Is it possible (=is it possible to create
> filter for it?
Well.. not really - you can try something like:
+* -*/*.* +www.yoursite.com/* +*.gif +*.jpg +*.css 
+*.js

(include EVERYTHING, then exclude ALL files with '.' 
inside, and include your website and some other 
related images or files)