Okay.
You can back up most of the data within the application itself.
For the address book:
Open it up and go to File > Back up address book. It will ask you where you want to save the back up to. When your on your "fresh" system open address book again and go to File > Revert to address book backup.
For the bookmarks:
Open Safari. Go to File > Export Bookmarks. Save it where you want. With your "fresh" system open up safari and go to File > Import bookmarks.
For the calendar:
Open iCal. Go to File > Back up database. Save it to where you want. With your "fresh" system open up iCal and go to File > Revert to database backup.
For your mail:
I can't really help you there. All my mail stays on the server so when I set up my mail account again it automatically gets downloaded again.
As for all your media files:
They are usually saved in your Documents, Movies, Pictures and Music folders. You can view these folders by opening the Finder. When I back up my iTunes i copy the whole iTunes folder. This allows me to save ratings and song play counts. When I am on my "fresh" system I simply open itunes and agree to the TOS. Then close it and copy my backup iTunes folder over the newly created one.
If you have any questions or need me to explain further then please let us know