Apparently Excel 2008 for Mac does not like the Shipyard spreadsheet this may also be true for the Wardogs Design Spreadsheet.
I have tried my best to keep the shipyard (and Wardogs Design) as compatible as possible but it would seem that Excel and Open office are determined not to work together.

At least at the moment Open office will open most file types.

I think that the solution could be to keep a version of Open Office that works for you on a 1GB usb flash drive. The drives only cost a few pounds. If you get a larger one say 4GB, you could keep a copy of your spreadsheets on it also, Although I think that Open Office only takes up 240MB.

Don't forget to keep a back up of the files.

It is possible to use Open Office from the usb drive without installing it on the computer.

See:http://portableapps.com/apps/office/openoffice_portable

I believe that you will find version 2.4.1 as well as 3.0

Paul