He didn't appear speaking on the screen. When he is first noticed ("My God, it's Prospero, who..."), we had a still of Prospero, looking menacing. He then dramatically appeared at the airlock door. When he told the story of him and Gloria, we played a silent film taken on camcorder and edited fairly simply (friendly computer geek had a copy of FinalCut editing software, but Adobe Premiere Elements will do the same), which had been taken beforehand. This also gave scope for humour (eg. "I had almost cracked it" at which point a picture of bottles marked 'u', 'v', and 'w' factor on lab desk. Amusing shot of Prospero tied up with gag and Gloria standing triumphantly over him)
The narrator was done the same way, but with the sound turned up. Again, prerecorded. Once on disc, all these clips, still and action, can just be embedded on a powerpoint slide.
We chose to do Prospero this way so that we didn't have any problems with the sound, or him not being able to hear/see the orchestra during his song.
I did get a few clips from the website you mentioned. There are some good sound effects available cheaply from www.sonomic.com (and we also had someone with a "Star Trek" sound effects cd, which apart from some explosions, had great "bridge running sound" and door opening. If you PM me with you address, I could send you a copy). For exploding planet at the end, I believe it is possible to take Alderon exploding from the original Star Wars video and digitise it, but there are probably copyright issues, and I wouldn't recommend it on this forum

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Give yourself plenty of time to do all this. I was forced to do it all in 3 days, due to unfortunate events (director's incompetence). I am not a computer whiz in any sense, so it's not that difficult!
Hope this helps, and good luck!