Add this bit of code in the <head> section in the top portion of your template:
... some stuff ...
... more stuff ...
That should enable the read-more capability.
Then, in each post, you'll need to add two snippits of code. The first snippit goes where you want the break to occur and the second at the end of the post:
This sentence appears in main blog.
This and all following sentences appear in the archive until this appears:
I can't guarantee this will work because your template may be different from what I've worked with, but this did it for me.
This post was written by Kevin