Speed up spreadsheet calculations

Ok so I have got a spread sheet I have been working on actually working now, my only problem is that the sheet is really really slow. It isn't too bad on my pc, but on the peoples machines that this will be run on they have excel2003 where as I have 2010.

It currently takes about 5min to fully load on 2003 where as it takes about 30secs on 2010. (I know 2010 can perform 1024 calcs at once and 2003 can only perform 1) however I need it to work well on 2003

Does anyone know how I could make this work but a lot quicker?

Hope you can help it is death defyingly slow at the moment!

Cheers Andy