I would recommend opening an account at emigrant direct over ING direct. The interface is complete crap at emigrant, but the interest is unmatched.
And to asnwer your question, no you do not need a large sum of money to start buying and selling stock.
Firstrade.com for instance, has no minimum starting balance. But for stocks... well, it's not easy money. I personally would recommend just socking it away in an emigrant account, but that's just me.
Good luck.