The short answer is that Office 2008 for Mac is a weak imitation of Office for Windows.
Options:
- Run a Windows virtual machine on your mac. Use software like VMWare Fusion, Parallels or VirtualBox to create the virtual machine. Install Word for Windows on the virtual machine. You will need to pay for licenses for Windows and Office (on top of what you've already paid for Office for Mac)
- Try OpenOffice or other alternatives to Word and see which will play nicely with Word's equations.
- Wait until later in 2010 for the release of Office for Mac 2011. Hope that it plays better with Word for Windows.
None of these is a simple solution.
The virtual machine solution is the most likely to just work after you get it set up, but setting it up will take some time. The OpenOffice solution is quick (and free) to try, but may have some compatibility issues opening and re-saving documents. The Mac team at Microsoft has lots of great things to say on their blog about the next release of Office, but I'll believe it when I see it.