According to the Mactopia website, the new Messenger 7 for Mac is designed for use on either older PowerPC Macs, or the newer Intel ones:

Messenger for Mac 7 is an integrated communications client that enables you to communicate with contacts within and outside your organization. Messenger for Mac 7 is a Universal application that is built to run on both PowerPC-based and Intel-based Macs and makes it easy to take advantage of the full power of real-time communications.
For personal Windows Live account users, Messenger for Mac 7 includes the following new features:

• Customize your contact list with nicknames that you choose
• Use Bonjour to see other Messenger for Mac contacts who are online and near your location
• Search for contacts in your personal contact list

Apple, Mac, Mac OS X, Messenger, Messenger 7, Mactopia