All of my macs are PPC based, are the DMG files Intel only? If that is possible.
Also, once I update, if something happens to my iPad 2, will the retail store still take it back?
A DMG can be expanded on either platform.
Remember, though, that this is beta software; It won't be as stable as the OS you're already running on your iPad. For example, you'll find that Safari will crash for no apparent reason in the middle of browsing. You'll also find that videos won't play properly, etc.
Things like this are to be expected in beta software, so you should think carefully before installing.
Also - in oder to install iOS 5 beta, you'll need to first download and install a beta version of iTunes (also available through the developers portal).
If you're not a developer I'd recommend skipping this initial beta and either waiting for one of the upcoming updates or even for the full release version.
RTP.