Hi! I've just registered into the forum to try to clarify things a bit, as I have the same problem and I think I know why IceGotic complains about it.
What I used the "details pane" in WinXP for, was to select one file at a time and find out if they would fit into a dvd. This was very easy in WinXP, as in every file selection that "details pane" would update, letting you know the total size of the files selected.
Is it clear now? I think it's a very useful feature, that has been sadly taken away.