First, whenever you discover you edited and saved an email attachment, try not to open it from your mail application again. Doing so, might overwrite the edited file with the version from the email message, which will discard your edits. Fortunately, most often a newly opened file will get stored in a different temporary folder, so this might be your lucky day.
Windows Explorer will not show the true contents of the Temporary Internet Files folder. Hence, if you know part of the file name, you need to use the command prompt:
Hold down the Windows key and press R (this opens the Run dialog)
(and hit Return to run it)
dir c:\filename*.* /s /a /od
filename is the start of the file name, followed by an asterisk (wildcard) to find all possible combinations of the name. The
dir-command will scan your whole hard disk and might run a long time. When it's done, it lists all files that match that name, with the newest file at the bottom of that list. That's most likely the file you want.
To copy the results from the command prompt, you might first need to click the top-left icon of the command prompt window, and select something like "edit » mark". Then, select the output using your mouse, and when the result is selected, press Return to copy it to your clipboard.
Paste just the filename you found into Windows Explorer, and if all is well, Office will open it. Now use File, Save As to move it to a better place.
If copying and pasting the results did not work, type 'cd' followed by the directory in the command prompt, this will display the items in that particular location. Now type 'start' and the file name with extension to run your lost document. For example 'start amanda.doc'.