Primary & Secondary phase are the CD versions, 6 in all, containing the entire radio series. You can buy them (I did about 2 months ago) from http://shop.douglasadams.com (I think that's the site - Tony already linked to it earlier) and I think the BBC have recently announced a deal with Amazon(.co.uk at least) so you might be able to get them there. (just checked - you can!)

(Sorry I don't have time to check all the above too closely, I'm waiting on a taxi which should arrive any minute!!)

Geoff
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Got one of the first Mark 2 empegs...
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Geoff
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Mk1 Blue - was 4GB, now 16GB
Mk2 Red - was 12GB, now 60GB