The NOAD reports the following notes about should and would:
The traditional rule is that should is used with first person pronouns (I and we), as in I said I should be late, and would is used with second and third persons (you, he, she, it, they), as in you didn't say you would be late. In practice, however, would is normally used instead of should in reported speech and conditional clauses: I said I would be late; if we had known, we would have invited her.
I thought that should and would really had a slightly different meaning. Am I wrong?