Added web 2.0'ish license agreement popups on SDN5: try any paid product download, like the Sitecore itself (SDN and download access required). It's not intended to hide actual download location, and in fact is unobtrusive.
Done with modalbox, which worked out well. The only issue we've spotted so far is that the page is moving underneath the modal overlay because scrollbar disapears in IE. Let me know if you see anything else.
[A classic "look what I've done post"]