Where would you find information on how much cash each brokerage firm has put aside to secure its customer's funds. I think this is called the firms "segregated account".
Also is this with the clearing firm they use or somewhere else?
Go with a bigger firm, such as RCG, Mann, IB, but keep in mind this does not guaranty anything. Refco is a perfect example. The key is to keep as little money in the account as possible and sweep it at least once a week.