Just been reading on Matt Bethers blog on a technique by  Már Örlygsson on a great way of doing popups (disclaimer: I know, popups are evil...fall of civilization...STDs etc....), which if you *really* have to use them is just the best way I've seen - especially as it would *seem* to be more accessible than other methods. Oh, and there's some great comments on that post which cover all sorts of other issues.