The prophecy states that the Dark Lord will 'mark as his equal' one of the two boys who fits all the criterea of the prophecy. Well, Volde did not hear this little bit of information. He set off, his arrogant self, to kill young Harry and rid his life of trouble. Well, he encountered one teeny, tiny, insignificant problem, he hadn't heard the whole prophecy!
When Volde tried to kill Harry, he ended up marking him as his equal. This had to be done before he could kill him. To make him his equal, he had to transfer powers to Harry he wouldn't otherwise have had (IE, parsletounge, ect.). After trying to kill Harry, Volde was reduced to nothingness, weak. Very much like young baby Harry. As Harry grew stronger, so did Volde. Equal in strength now, but not skill.
The final duel between Harry and Volde cannot happen until book 7. For them to be 'equal' Harry has much to learn. He will need at least a year and a half more of school to be able to stand up against a full-strength Volde.
Now, none of this is certain, just my speculation. One thing is certain, at least one of them will die, and we'll have to wait 2 more books to find out who...