On the mailing list and IRC there are many questions about Cassandra internals. I understand where the questions are coming from because it took me a while to get a grip on it.
However if you have a laptop with a descent amount of RAM 2 GB is enough for 3-5 nodes, (4GB is better). You can kick up a multi-node cluster right on your laptop. Then you can test failure/eventual consistent scenarios such as (insert to node A, kill node B, join node C) till your hearts content. http://www.edwardcapriolo.com/roller/edwardcapriolo/entry/lauching_5_node_cassandra_clusters
