In American English, "talk to" and "talk with" are essentially the same, but can carry additional implications depending on context:
"Talk to" is frequently used to start an instruction for obtaining information from a specific person or group, as in this exchange:
[inquiry] "Where can I find Sarah McLeod?"
[response] "Talk to the clerk at the second desk."
"Talk to" can imply a circumstance where the listeners do not have the opportunity or permission to respond.
"Talk to" can be synonymous with "instruct", "lecture" (especially when correcting someone's past behaviour), "console" (verb form), "guide" (verb form), or "teach".
"Talk with" generally implies an exchange of ideas, such as in equal conversation.
"Talk with" can be used euphemistically instead of "talk to" if the speaker wants to imply an equal exchange where there was none.
Some Americans demonstrate a preference for "talk to" when describing what they are currently doing, especially if they are doing it via a medium such as telephone or internet ("I'm talking to Sarah."), but are more selective about the propositional sense "("I'll talk [to|with] Sarah."). Perhaps "talk to" is slightly more intelligible when unceremoniously bellowed down a flight of stairs toward a parent or while trying to be heard over construction noise.