Excuse my Aussie bias ...
I'd hang onto Ponting if I was you - he's already made a century and a 90 odd so far and after Aus thumped South Africa on Sat they are firming is as favourites.
Lara's done nothing so maybe look at another top drawer bat, like maybe Hayden (fastest ton in world cup history against the number 1 ranked ODI side in the world). He also made 182 not out against NZ in the series just before the world cup in NZ.
Pietersen would be another good bet as a batsman. Some of those names in there I've never even heard of!
I'd be tempted to get rid of Glenn McGrath as well. He's not performing at his normal level and I htink someone like Tait would be a better bet. This could be his coming of age in the World Cup - he had a great game against the Saffa's and took some vital wickets.
Hang onto Murali, he'll consistently pick up wickets and the pitches will suit him.
Who the hell is Hurdle?!