G4TV has a new article out about the Electronic Arts press conference at the GCDC ’08. In the article it says:

9:40AM – […] Then he shows a new trailer for Harry Potter and the Half-Blood Prince game, and James and Oliver Phelps, who play the Weasley twins in the movies, come out and play it. Castable spells, potions, story play, Quidditch. Pretty amazing looking.

If I find any more information I will post it! Thanks Renata!