i use scottrade. it's only $7/trade. there are even cheaper ones available. i think sharebuilder might be one. there might be a $500 minimum to open an account though. shop around.
yahoo has some good research tools available also, if you just want to look into some stocks before opening an account somewhere.
as bdb says, $200 will not grow into a nest egg that you can retire on, but it's a start. if you can put that much into stocks every month, it will get you in the habit of funding your trading account. also, even if you only have a few shares of a stock, that will drive you to follow the company closer, which will help you make decisions down the road as to when to sell the stock or buy more.
if you want a great place to get some advice, i'd strongly recommend the motley fool. just go to fool dot com.