Mouse should work out of the box, but you won't get the controls to assign button actions, etc. Try doing a clean install, then just use the mouse without the software to see if it works and doesn't crash your box. If it still crashes, either you got a bad mouse or the g5 will need a code fix. Otherwise, you should call Microsoft and tell them that they'll need to update their software.
Also be sure to get your software from the website if possible rather than the CD. A new version may have been released since the CD.