David, the "seed" would be a full BZR repository, so you could just unpack it into a directory, do `bzr update` and be done. No conversion needed. My understanding is that as far as the _basics_ are concerned, bzr is similar to git and mercurial. You can have "lightweight checkouts" but that isn't what I'm suggesting here.
John, I think it would be very good for you to have a copy, and it would be very good if we can work out instructions that you can follow which we can put on the wiki. The starting point is to ask what operating system you're using.
David: it is, I'm pretty sure, easy to convert between different DVCS's, even on the fly. So the fact that I use BZR as the host repository doesn't mean that others have to use BZR to download it to. For someone who is ... er ... "non-technical", such as John, is there a DVCS that is easiest to use?