Publishing post summary in sidebar

Hi,

I’m looking for a way to publish posts (or post summaries) of a certain category in a sidebar on the home page but then, when the link for the post is clicked on, have the full post appear in the main post column.

I found a way to get the post to publish in the sidebar by basically copying the entire post code plus a category slug to the sidebar, but then when you click on the link the full post is visible in the sidebar, not the main post column…

Any ideas?