It's easy to get iPhoto 6 and iWeb installed on your G3 by copying the iLife installation package to your desktop, control-clicking on the package installer, picking Show Package Contents from the pop-up menu, and then removing this code from the Distribution.dist file using TextEdit:
// Rule out insufficient hardware
if ( !hasAcceptableHardware() )
{
my.result.title = system.localizedString('TITLE_INCOMPATHW');
my.result.message = system.localizedString('ERROR_INCOMPATHW');
my.result.type = 'Fatal';
return false;
}
iPhoto 6 works great on my fast G3 (1GHz) upgraded Mac (though there are no advanced editing features). iWeb works as well, and it does have the advanced image editing features enabled, but they're very slow.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060118175207264