If I attempt to open a .xls with Excel 2003 via Windows Explorer,
Excel opens, but the sheet is never displayed, I receive a windows
error message stating the correct file lactation, but that the
specific file can not be found.

If I then repeat the same process, double click the .xls in Windows
Explorer, Excel will open the file. If I have already opened Excel I
can use the fileopen menu to select any .xls and it will open.

I suspect the problem may be with windows explorer, but users of Excel
may have experienced this problem.
Vista SP1 and Microsoft Office 2003.