Here are some quick solutions that worked for my setup of backtrack 5 gnome 64bit

1. To get the database to load with available db_drivers, just start metasploit msfconsole from the terminal or run from the backtrack menu if you are root.
2. When you try to run an auxillary module or scanner you receive an error about pcaprub not being loaded.

My solution

Compile the pcap module from the /msf3/external folder:

1. ruby extconf.rb && make
sudo make install

2. cd /usr/local/lib/site_ruby/1.9.2/x86_64-linux
cp /opt/framework3/ruby/lib/ruby/site_ruby/1.9.1/x86_64-linux