For future, you should definitely follow Suzanne's advice and save the file
to a document folder before working on it.
But you may still be able to find the file you've been working on. First,
try opening up the same email and re-opening the attachment. You may find
that it has retained your changes (I have seen this happen with my own
documents before).
If that doesn't work, you could also try opening up any email with an
attachment. Right-click the attachment and choose Save As. Now, without
changing it, take note of the pathway it wants to save to (on my email, it's
always an OLCK or something like that). It will be a long convoluted path -
maybe something like C:/Documents and Settings/Your User
Name/Microsoft/Outlook/...etc. (I'm just making that up, but it will probably
be something similar, and several folders deep). Write down the paths, then
click Cancel (unless you really do want to save that attachment).
Now, open up Windows Explorer and navigate to that same folder, and check
for your original file name. Open up that file, and if it's the correct one,
immediately save it to a normal document folder so you can easily find it
again.
Again, this isn't an ideal way to do it - you should save to a document
folder before working - but it may help you recover your file if you've
already spent a lot of time working on it.
Hope this helps,
Jen