Assuming that you were using the Excel 2007 native file format, then there is actually more than one file being created when you do a Save. The .xlsx file format is a zip archive of several different files, each covering a different aspect of your workbook. You probably need to recover the full zip archive to be able to reconstruct your file.
When you saved the file, you didn't actually wipe out the old file. Rather, you erased its entry in the file allocation table. What happens is that Word or Excel saves the file with a random file name in an unused part of your hard drive. If the save is successful, it renames the saved copy with your desired file name--and erases any other mention of that file name in the same folder in the file allocation table. So if you can recover the file contents before those file clusters get rewritten, then the day will be saved.
Before paying money to see if you can recover anything, you might want to download some free alternatives (ideally onto a flash drive) first.
http://www.download.com/Restoration/3000-2094_4-10322950.htmlThe above free program, called Restoration, is small enough to run from a USB flash drive, floppy disk or a CD. It doesn't need to be installed on your hard drive and possibly damage the free space where your deleted files might reside. Restoration can undelete files that were removed from the recycle bin or directly deleted from within Windows. You can scan for all recoverable files, or you can focus on a particular file by entering part of a file name, an extension or a search term. Restoration works with FAT and NTFS as well as digital cameras cards.
WinUndelete $50. Free trial version available.
http://www.winundelete.com/download.aspFree Undelete (freeware).
http://officerecovery.com/freeundelete/
