Import a Bitcoin account
Your wallet.dat file records all of the important information. I don't know if the other files also contain confidential information, but two things are sure:
- Your private keys are only stored in wallet.dat. If you keep that file safe, and all of the other files get leaked out, nobody can steal your money (though they may find out other things about you).
- The wallet.dat file contains everything you need to recover all of your money, as well as your address book. If you delete all the other files, and just keep wallet.dat, you will still have all your money and all of the addresses in your address book.
The other files are mostly just the downloaded block chain history. If you lose those, you are in for a big download, but nothing too serious.
It looks like you do just have to backup/transfer the wallet.dat file.
From their FAQ:
How do I backup my wallet?
Your wallet.dat is stored in the directory ''%appdata%\Bitcoin'', which is typically:
Windows XP: C:\Documents and Settings\username\Application Data\Bitcoin
Windows Vista: C:\Users\username\AppData\Roaming\Bitcoin
Linux: ~/.bitcoin
You need to make a backup of the wallet after every transaction, as the old backup file will be partially or fully invalid. Wait at least a few seconds after your last transaction before making the backup.
If you want to encrypt your backup, you can use some program like TrueCrypt. An in-built tool for encrypting your wallet will be included in Bitcoin later on.