Take a screenshot of a QuickTime movie frame

If you have QuickTime 7 Pro, this is as easy as copy and paste.

• Open both videos in QuickTime
• Select and copy the contents of one video (⌘+A, ⌘+C)
• Switch to the other video and move the playhead to the desired insertion point (e.g. the beginning or end) and paste (⌘+V)

Then you can save the combined movie.

Of course, it is likely you don't already have QuickTime 7 Pro already installed. Apple charge extra for QuickTime Pro (£20) which may not be worthwhile for you if you don't use it much. Also, if you are using Snow Leopard, that includes QuickTime X which doesn't have a Pro version available. In that case you'd need to install QuickTime 7 in addition to QuickTime X.

I imagine there has to be a way to do it with iMovie as well, but I don't have experience with that. Perhaps someone else might.

Usually, Apple put it's keynotes in iTunes Podcasts, where you can download them.

Look for Apple Keynote and download the ones you want.

Just note that there might be delay, often less than a week, before they released the latest keynote.