You may try NeoOffice. It will open Excel 2007 files. However, I don't know if it will open macro-enabled files. Download it and try. If NeoOffice can't do the trick, then your only other option is to buy Office 2008.How can I open an XLSM file (not XLSX) on my Mac? I'm running OSX 10.4.10 and have Numbers, Office '04 and the Microsoft Beta converter thingy installed, and nothing will open this file.
Cheers