You could always use the HTML -title attribute. Something like:

my @title ({title=>'Option 1', value=>'Option 1 help'},
            title=>'Option 2', value=>'Option 2 help'},
            ...
          );

print checkbox_group({-name    =>'my_name',
                      -value   =>['Option 1', 'Option 2'],
                      -default =>'Option 1',
                      -title   =>"$title->{value}"}
                 );
[download]

I'll leave the exercise up to you as to how to get break the content out of @title, but that should be easy enough. I'm using this in a few places, though not with the same idea in mind.

When you hover your mouse over the option, it will pop up the standard HTML 'tooltip' element. The added benefit of this is that you're not pushing the user off to another page or using popup windows or javascript, and it should work in text, WAP, and PDA browsers.

Note, this may not be properly supported in all browsers.