Update: Thanks for visiting my blog. You landed here because you were looking for a way to have expandable posts. This entry, however, is five years old. It still works, though, so if you want to do it this way, you can. However, it may be better to just use the <!-- more --> tag. This adds a break in your post that does quite the same thing.
I've just managed to reinstate the expandable posts using the new Blogger template. The method is quite similar to the old Blogger. However, owing to the somewhat complicated (okay, newer) structure of widgets and tags, placement is a bit more sensitive.
Here's how I did it.