Tunelblick-3.0_B04 expects them to be in the $HOME/Library/openvpn/ folder. This folder is automatically created as mentionned on the http://www.tunnelblick.net/ website.
Replace $HOME with the full path to your home directory ("echo $HOME" in a Terminal.app window)
I discovered that it is best to specify the complete path for the ca.crt file. Put the next line (without the quotes) in your openvp.conf file: "ca $HOME/Library/openvpn/ca.crt".
The /Library/openvpn/ direcory is displayed differently in Finder according the language of your Desktop e.g. "$HOME/Bibliotheek/openvpn/" when your Desktop is in Dutch.
As said, this is only a different display name !
Do not use this name in your openvpn.conf file !
Just open the Terminal.app and do a "cd $HOME/Library/" followed by a "ls" to display all the files and directories.
P.S. Tunnelblick-3.0 is based on the old openvpn-2.0 version which does not support usb-dongles (keys). For an installation of openvpn without GUI (Tunnelblick) look at: http://girasoli.org/?p=30 website. I used it with MAC OS X 10.4.10 and it works fine.