Excel 2003 Open Shared Worksheet over Internet??

Hi, I don't know if anyone has ever done this successfully but here goes nothing. I have a shared Excel 2003 worksheet, over my local network it works fine. However, I also have the file on our web server and been able to open it at different locations by simply opening the http:// address to the Excel file (in Excel), however, although it will open the file fine, it will only allow read only access on the second opened file.

Does anyone know if I'm missing some basic fundamental process to achieve this or if I need to set different permissions or indeed anything to be able to the two to act as they do over the network?

Any help is gratefully received.

Thanks

Paul