The opened hotmail files are stored in your browser’s Temporary file folder. The whole problem is that the opened file is not saved as the actual document name.
For example if the attached file is named test.xlsx the file in the temporary Internet folder will be called something like – GetAttachment.aspx?file=ecf277… It will be a very long string of characters without the obvious excel extension.
So if it is Internet Explorer that you are using, then the temp files are located in C:\Documents and Settings\YOUR PROFILE FOLDER\Local Settings\Temporary Internet Files. When you have located this folder look for excel icon files that have been modified at the time when you were editing your file and then double click on that file, which will open a internet browser and will fetch your file. Although I must say when I have tried to recreate your situation the changes that I have made in the excel file have not been saved.
Also I would suggest not editing and saving repeatedly from within your email. Copy to documents and edit and save there and then attach the finished file to an email addressed to yourself. Then move the file with attachment to a folder.