If you think this might be the problem, try temporarily switching the scanner off.
See MSKB 262530 Under some circumstances Excel will recalculate your workbook when it opens or saves it.
Excel 2002/2003 has advanced encryption methods which may slow open and close for protected workbooks.
Where possible make sure all your workbooks have been saved by Excel 2002/2003, and avoid having some users on previous Excel versions.
If you have upgraded to Excel2002/2003 from an earlier version and you have Norton Antivirus installed the integrated virus checking may cause slower file opening.
Often its faster to open a workbook than read the links from a closed workbook.
Some virus scanner settings can cause problems with open/close/save, particularly on a server.
Make sure you have Find Fast and Fast Search turned off.