Granted you still need a Mac with OS 10.3+ to set up an Xgrid controller, but I’ve been sucessful in using Intel & AMD based systems as Agents (nodes) in an Xgrid cluster at home to render blender projects.
I used a PIII 867 with FreeBSD 5.2 installed and the xgridagent program from sourceforge http://www.sourceforge.net/projects/xgridagent
Also I tested the JAVA Agent appliction on an extreme old AMD K6-2 400 with Windows 98SE installed and it connected and rendered frames with my Powermac with OS 10.4-Server installed acting as the Controller. Although I’m not sure if that system didn’t slow the rendering process a tad…
So if your running in a mixed enviroment or thinking about building a home cluster, you can run Grid with a mix of OS’s and processors…