iWork would be very difficult, but Word for Mac is doable. It also depends on which version of Word for Mac - the Office 2008 version doesn't have VBA, only AppleScript. It's said that VBA will be back in later versions of Mac Office. If you're going to do this and move all the templates to Mac and not use them on Windows again, porting things to AppleScript would be the way to go. If you're going to leave them on both PC and Macintosh's, sticking with VBA is the way to go (but not on Mac Office 2008!).
The first is that Macros can be either WordBasic or VBA (Visual Basic for Applications) - they won't be Visual Basic as that is outside of the Word environment (although Word can be automated from VB). Macros are just one or more routines written in WordBasic or VBA. WordBasic is really, really old and not used much, so the majority of your conversion will probably be from VBA.
No matter what, you'll want to convert out of WordBasic into either VBA or AppleScript. Here's an article that shows some conversions: http://www.standards.com/OhMyWord/ExampleWB2VBA.html
If you're running VBA on Mac Word (not 2008!), almost all of it should work just fine. There are a few things to change, like how you work with files and diretories, but not much more than that.
If you want to convert to AppleScript, it takes a bit of work. There is a good transition guide on http://www.mactech.com/vba-transition-guide/index.html (you have to subscribe to get it).