IMDb poster, steveg 1023 had this to say about Matthew Macfadyen's role in Frost/Nixon.
...I also was lucky enough to see a screening and take part in a group Q&A with Ron Howard.
MacFadyen's solid, but he really is a supporting role in a movie that really belongs to Sheen and Langella. HIs character is very Darcy-ish in the sense that you know there's a lot of emotion brimming under the surface, and it only comes out in controlled outbursts. He serves as a nice foil to Sheen's emphasis on charisma and a playboy attitude.
He gets one of the best moments of the movie, though. It's quick, but I don't want to spoil it.