Opening .TOAST files

Your information is correct. .toast files are disk image files that have been created by Roxio Toast. Toast is disc authoring software that does more than just burn discs.

You can either buy a copy of Toast (it's awesome software) or you can ask whoever gave you the .toast file to get you the data in another format. Disk Utility will make a .dmg image file of a data disc, though it's not the thing to use to make an image of an audio disc.

Bottom line, you have a Toast disc image file and you need Toast to use it.

I think it is corrupted, or at least partially missing. The .toast files have resource forks, which is additional information from the usual data part of a file. Resource forks will transfer along with the data fork when you use most Apple-style copying techniques such as the Finder. But if you've transferred it over the internet, say with FTP, you will often lose the resource fork of a file.

I have never been able to resuscitate a Toast image file that is missing its resource fork.