Which Java version to target?

Are there any up-to-date statistics available that give a good idea of
what Java version most web users have installed on their machines?

I'm developing a java applet as part of a web site, and I'd like to
know that most users will be able to view it without any issues - as it
is, if I compile it to target JDK 1.5, all the machines other than my
own that I've tested it on won't load the applet, and worse still,
don't give any sensible user feedback as to why.  I accept there will
also be a percentage of users with an exceptionally old java version
installed (or worse still, none at all), but I'd like to keep this to a
minimum without sacrificing too many features that come with the later
java versions.