Welcome to the forums
Jiri and I have a bit of previous in the Alien world - glad that you tracked down the OT !
Indeed Luke (klokwerk) - I've got those two discs as well - they were going around Ebay back in the day and "The Archivist" the chap who originally put them out there, had a far jazzed up menu and selection screen courtesy of my good self put on his discs. However the quality of the items are not 100% as you have (both) rightly said. The Making of Aliens is only missing about 30 seconds pre-end credits. So its not so bad - but similarly I'd love to find a full version of a higher quality.
I'm sure there must be a better version of Giger's Alien out there, ideally sans subtitles. You'll also notice that from Disc 2: Alien Director's Cut Documentary - Presented by Danny Boyle - is out of synch. Bizarrely I spent my morning correcting this, so there is now a fully synched up version available. I'm sure there must be a UK user with a better version out there.
Jonno - similarly welcome to the forums ! Switch on your PM's if you are prepared for a bit of interest coming your way no doubt !
Night chaps,
meedermow