You can get cassandra at cassandra.apache.org and the ruby gem by running:
gem install cassandra
I did run into a problem with the trift_client gem when installing. If you get a Load Error, run this.
sudo chmod 644 /usr/local/lib/ruby/gems/1.8/gems/thrift_client-0.6.3/lib/thrift_client/*.rb
sudo chmod 755 /usr/local/lib/ruby/gems/1.8/gems/thrift_client-0.6.3/lib/thrift_client/connection
Here are some of the Cassandra commands from the video:

connects to the cassandra server using the Twitter keyspace

store = Cassandra.new(“Twitter”)

create a new column family in the Twitter keyspace called Users

cf_def = CassandraThrift::CfDef.new(:keyspace => “Twitter”, :name => “Users”)
store.add_column_family(cf_def)

add or create a row to the column family

store.insert(“Users”, “cmaxw”, {“name” => “Charles Max Wood”, “description” => “Awesome coder”})

remove a column from a row

store.remove(“Users”, “cmaxw”, “description”)
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