That file can later be read and displayed by Internet Explorer.
I use Win XP Home SP3 (32-bit) and IE7 (and get the regular updates).
I noticed yesterday that all my .mht files coming from the geocities.com site (Thinker) could not be displayed any longer:
Internet Explorer displays the "Invalid Address" screen and shows the address http:///js_source/adframe07.html
Any idea what happened? (some tightening of javascript security rules?...)
Note, on the weird/funny side

if I copy the .mht file from my C: hard disk to my other D: hard disk, or to USB memory stick, or to diskette, the file can be displayed by IE from these other devices without any problem!