Editing post author & date…

Regarding the post author… What is the best way to go about changing the post author name for all the posts in a specific category. For ex., the posts that show up on the home page display the name of the user login. How can you change this to display something else.

As far as post dates… If you are posting articles that were written several months before you are uploading them, and you want the actual date it was written to show instead of the date you uploaded the article to the site.. how would you go about that?

Is there also a plugin that allows you to change post author & date for each individual post?