Applets (like this one) worked for me just fine in Chrome on OS X 10.5 until I had a recent Chrome update (to 13.0.782.220) and an OS X Java update (10.5 update 10).
Things seem to work just fine in Safari. I had some trouble in Firefox until I followed suggestions from this other question and made sure that I had Java 1.5 32-bit enabled using Java Preferences.
You can't see it in the context of the example I linked above, because that applet is set to have a width and height of 1 pixel, but if you expand it out to something like 200 x 100, it gives the message "No plugin available to display this content." So it looks like Chrome can't find the plugin.
Is there something magic I have to do after a Chrome or OS X Java update in order to help it locate what Safari and Firefox can find?