I think Mr. Dastard may have it there, index.dat is the file which keeps track of all your temporary files used by Internet Explorer.
Do you have another web browser like Firefox or Opera on a disk e.g. a magazine cover disk? If so switching browsers could be an immediate fix for getting your messages, you could then fix Internet Explorer at your leisure - you will only want it for downloading MS updates once you use Firefox or Opera :-)
If you don't have a disk you can download a browser via ftp from the command line in windows. As far as I know it will not be impacted by any index.dat issues (
http://culearn.creighton.edu/utiliti...ommandline.htm) as background in case you've not used it.
Good luck.