Well, the NASDAQ is the name of the actual exchange, the DOW Jones Industrial Average is an index used to measure the 30 largest companies.
But yes, most worldwide exchanges require a minimum tradable parcel of $500 in value, depending on the price of the shares. As for finding a broker, I use the Australian ETrade, which is fairly cheap for over here. You might want to check out a site like this one here [http://www.online-broker-guide.com/] to get a good idea of your options out there.
If you already have a savings account with a big bank, a lot of them offer a trading platform as well, and it would generally be easier that way (no transferring funds into the third party account to trade with, access to your portfolio through your online banking screen and no 4000 character passwords to get in, and of course, the physical bank branch you can go to for help.)
As far as trading commodity futures, you definitely need a few thousand dollars before you can start, so saving up would be the only way to get in there.
But yeah, I bought shares with my tax return and I'm up 16% in a month. Much tastier than savings account interest or a term deposit ^.^
