PowerPC is an older type of processor used before Apple switched to Intel chips.
There was never a MacBook that used PowerPC chips so that's an odd error message.
What you're probably seeing is a message stating that Office 2004 will work only with PowerPC Macs, so it won't run on later Macs like your MacBook.
You'd be better off with a later version of Office for Mac, such as 2008 or 2011.
A new version (Office for Mac 2015) is expected next year.