I heard that they now can handle Office 2007 PowerPoint files too.
And, I wouldn't go bananas at Bill Gates over the decision to create an XML (more open) file format. Microsoft has done plenty of stupid things, but replacing a 7 year old closed file format isn't a bad thing. And aren't .wps and .wpd from Word Perfect and MS Works?
Anyway, back on task...
http://www.microsoft.com/mac/Look on the right side of the screen, third link down is the converter you need.
Works well. I use Office 2004, and iWork08. I'm able to open anything I need to.