Avoid duplicate posts

HI,

two questions regarding posts:

1) I want use on the front page the latest post module as follows:

a) one latest post module for all categories and addtinionally
b) one latest post module for each category

Question how to avoid duplicate posts ? E.g. the very last post belongs to the category "history". That post appears in the latest post module for all categories and in the latest post module for category "history". The post should be only appears in the latest post module for all categories.

2) The latest post module should have a short description for each posts, which is appears only in the latest post module. In the blog should be not visible. How to do it ?

Thanks,

Michel