I notice that the original question has only been answered partially.

saying:
if you win 1 million dollars, please give me some
This definitely and correctly refers to a future possibility.

saying:
if you won 1 million dollars, please give me some
the phrase refers to a past fact, i.e. the beggar has been told that you won.
The other possibility is the past subjunctive mood. In that case the first part of the sentence would refer to a hypothetical (irreal) possibility (like "if I were a rich man") - and your original second part would not fit it, as Branshea correctly remarked.