.mht is a Web Archive file.

From MS site: "A Web Archive file allows you to package a Web page and its supporting files into a single file. A Web Archive file has the .mht extension and does not make changes to the original Web page. You can use Web Archive files to keep track of supporting files. Or, you can send an entire Web page with all its supporting files packaged as a Web Archive file in an e-mail message."

Heres a few links but you could try a search of the MS site for more info.

http://office.microsoft.com/downloads/2000/Mhtml32.aspx
http://office.microsoft.com/assistance/2002/articles/oChooseFileFormatWebDiscussion.aspx

>Hi UTers,
>
>I just had somebody send me a document named gallery_view.mht. I copied the file to my laptop that has no intenet connection. I double clicked on gallery_view.mht and my browser opened with a page filled with several images. If I right click on the page to view the source I see html code with references to images ie:img src="_penta_right_m.jpg" width="280" height="260". What is this file. Are the images embedded in it? How do you make one of these files?
>
>Thanx,
>Neil