Recently one of the users was having this issue on his XP Professional machine with Office 2003 installed. When he tried accessing excel files on the network, they would take quiet a lot of time to open. This is the way i diagnosed/solved it.
1. The excel files on local pc would open fine, which suggested that the installation was fine, but still did a repair which did not solve the issue.
2. After some searching. i reached an article and the solution over there worked. Heres the explaination.
The reason why it opens slow is because of an Add-in called OFV ( office file validation ). What it does is that, before opening the file, OFV reads it to make sure its trustworthy. Now, when this is done over the network, the process takes time, and hence it takes longer to open the file. Disabling OFV solves the problem. Steps to do it.
1. Start-> Run-> Regedit.
3. After you select the key point to New on the Edit menu, and then click Key.
4. Type Excel, and then press ENTER.
5. Select Excel, point to New on the Edit menu, and then click Key.
6. Type Security, and then press ENTER. ( You might already be having the key security, if so skip the steps 3-6 and proceed to step 7 to create the key in Security )
7. Select Security, point to New on the Edit menu, and then click Key.
8. Type FileValidation, and then press ENTER.
9. Select FileValidation, point to New on the Edit menu, and then click DWORD Value.
10. Type EnableOnLoad, and then press ENTER.
Note: The default value is 0 which disables the validation.
11. On the File menu, click Exit to quit Registry Editor.
Now try accessing a network Excel file, which should open normally ( faster than before ).
Sources : http://support.microsoft.com/kb/2570623