Metaproducts Offline Explorer Pro from 
wwww.metaproducts.com claims to be the only Offline 
Browser on the market that will do this for streaming 
video and audio (such as .RA files). These types of 
formats cannot normally be downloaded by right-clicking a 
link and selecting "save target as" (IE) or by equivalent 
functions on other browsers.

Warning: This is commercial software, not freeware like 
HTTrack, but you can download a fully-functional version 
for 30-day trial. It gets disabled after the trial period 
is up. I tried it only once and forgot about it after that 
and the trial version has now expired on me before I had a 
chance to test the above claim.