looking to recover overwritten excel file on server used on workstation

I am most certain that you will not be able to recover that data (as it has been overwritten not deleted)  but you can use some of these tools
http://www.ontrack.com/index.aspx
http://www.runtime.org/
http://www.pcinspector.de/file_recovery/UK/welcome.htm 
http://www.snapfiles.com/get/restoration.html 
http://www.recover4all.com/download.htm
http://www.partitionsupport.com/

Also try if you can find a copy on the hard drive it happend to me to find an old copy.
try C:\ Documents and Settings\USERNAME\Application Data\Microsoft\Recent
C:\ Documents and Settings\USERNAME\Application Data\Microsoft\Office\Recent
and also do a serch on your pc for the file name and a maybe you can try a search for *.* and a word from the file if you can remember.

Also try XLS Regenerator
 http://www.download.com/XLS-Regenerator/3000-10743_4-10387551.html?tag=lst-0-2

When you say you can't get the file back from the server, what kind of server is it?  If it's Windows 2003 you may have Volume Shadow Copy enabled which will have an automatic version backup.

http://www.microsoft.com/windowsserver2003/docs/ShadowCopiesSharedFolders.swf

If not, the temp file wouldn't help much, but if the file was ever emailed to someone, the attachment would still be there.

Do you not otherwise have a backup of the file from a server backup?

Jeff
TechSoEasy