I've only seen the film at the cinema so I can't check it, but I'm pretty sure that the music playing during that scene is 'In The House - In A Heartbeat', a track composed for 28
Days Later that's since been used in a million other places (an exaggeration, but it does seem to be popular with the makers of TV-show and movie trailers).
To my ears it's the standout cut from the 28 Days Later soundtrack and, from memory, it's used four or five times in 28 Weeks Later (ie, more than it was in the original film).
You can check it out on YouTube:
http://www.youtube.com/watch?v=dMyIG2EKPoE
If I'm wrong about the track you're after, ignore me.
