With R & C, playing the first three titles doesn't really give any real benefit when playing future, except for a couple of in jokes. The games aren't really part of a continuing saga, they only feature the same characters (like james bond sort of)
With J & D i don't know, i've only played the ratchet games.
Sorry, i also dont know about whether R & C work on the 80Gb as I played them on PS2, but there's a website somewhere that tells you what issues they have.
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