It looks like the Billy Boyd rumor that you have been hearing about has been somewhat firmed up. This week in the Sunday Times an article appeared concerning his particiapation. Also in the article are a couple quotes from Jackson and a bit of history about the film itself. This is worth checking out. Here are some selected parts of the article.
“Then I was auditioning exclusively for Pippin, a character whose naivety and inquisitive nature almost add up to bravery,” says Boyd. “The second scene I had to read was when he was lost in the woods. I felt it went well but it was six weeks before my agent phoned and said: ‘Guess who is playing Pippin in The Lord of the Rings?'”–Boyd
“The playwright Ronan O’Donnell told me just to use the scripts, but that would take a braver man than me. So many people have read the books and have their mind set on how it should be played, you have to do your homework. You look on the internet and they are discussing scenes you don’t even know about.”–Boyd
“We have such great real locations that we don’t need to struggle too much to create Middle Earth,” says Jackson. “But one interesting approach we are exploring is to digitise the entire movie into a computer, every frame, which would allow us to fiddle with all our shots, adding sunsets, cloud formations or waterfalls – whatever is needed to make it feel magical.”–Jackson
Only Gollum, the twisted character sucked dry by the ring’s evil, will spring directly from the computer. “His performance has to be spectacular,” said Jackson in a recent interview. “It has to be way beyond anything we have seen to date. The Gollum design is finished. I’d describe him as not too fishy or froggy, but we have taken great care to make him believable.”–Jackson
Thanks to Aram over at Imladris for pointing this out.