How can I get popover-like behavior in Snow Leopard?
NSPopover is only available in Lion, but are there any good third party libraries to get similar behavior in 10.6?
Try Matt Gemmell's MAAttachedWindow. You can find it on this page:
Matt provides a link to a project using this with a NSStatusItem; it probably wouldn't be too much of a stretch to modify it to work with whatever you've got in mind.