I don't they should appear in episode ]I[.
Consider episodes IV - VI as the next generation.
Remember when Luke and Ben meet Han for the first
time in the Mos Eisley Cantina?
Han Solo was a smuggler at that time, nobody "important"
like a queen/senator Amidala or a Jedi Knight or something.
He was just minding his own business at that time not knowing
he was going to play a major role in destroying the empire's rule.
The fact that nobody knows him until his appearance in a new hope just makes it cooler.
Besides it would be too coincidental to play a part in Anakin's story / life time as well.
Isn't it way cooler to think he actually is part of the "new hope", not the film title but the words as you read 'em.
Same goes for Chewie and Lando.
When I first saw Empire I really liked the new idea of a new character: Lando Calrissian.
So I think Episode ]I[ should include new characters as well.
If Lucas has got the time for that anyway
he has a lot of explaining to do in 1 remaining movie! Tough job.
I say more new characters!