Well, the February 20th date is based on an Apple Recon article. From what my "friend of a friend" has told me, who also knew there was going to be no iLife or iWork at Macworld, Leopard is essentially complete. The stuff they're seeding to developers lacks some things that we won't see until it's officially unveiled. I'm not sure about the Video iPod, but it would be a nice accessory to a simple OS announcement, and that's why I mention it. I would say the only thing to hold me to is Leopard on the 20th. That's just a hunch, though, and I have nothing to back it up other than the Apple Recon article. As far as the iPod goes, I simply think the technology is there and the iPod line needs a refresh.
If the February 20th thing is true, count on invites going out to press on the 13th. When the Mac Mini and the iPod Hi-Fi were announced, the invites were sent out exactly one week prior.
OK, fair enough. Good guesses. BUT, my thinking is that, this being a Developer's conference, and the invitation being formatted the way it is, Leopard is at least going to be previewed at the conference, if not released.
Possible new Macs, but with the recent huge announcements of the iPhone and AppleTV, I doubt we'll see any iPod updates/releases at the conference. Apple has started to separate it's "Mac" from it's "iPod" announcements, and the Developer's conference usually is more Mac-based.