When open excel attachement files in outlook express,
there is an error prompt :
"windows cannot find C:\Documents and
settings\username\Local settings\temporary internet
files\content.IE5\0.1QFSHUV\filename.xls.
Make sure you type the name correctly, and then try again.
To search for a file, click the start button, and then
click search."

I cannot even open the file even if i save. pls help.

What happens when, in Windows Explorer, you highlight and double click on a file with extension XLS? Does it Excel start and open the file

If yes, verify that the folder given in your error message actually exists, that the attachment is indeed an XLS file and not one with just extension XLS
If no, then your PC is not configured to associate XLS with EXCEL.EXE: you need to set up this association. In Windows Explorer, click Tools + File Types - what needs to be done should be fairly obvious. If it isn't, contact your IT support people.