Are you saying that if you re-create the workbook completely from scratch (no copying and pasting etc.) it is still slow to open? If so I would suspect that your copy of Excel is damaged. If you have Excel 2000 or 2002 try Help/Detect and repair.
What happens if you copy the file to your local (C:) drive and open it from there?
Try setting calculation to Manual, then opening the file, then pressing F9.
Does the file contain array formulas?
Are you using filters? - if so set them to "All" before closing the file. It should then open faster.