I just read that Japan was willing to surrender in July on the condition that Emperor Hirohito would not be tried as a war criminal, but Truman declined and the bombs were dropped...essentially making Truman evil. Given the amount of lives destroyed with the bombs, how accurate is this claim? Not trying Hirohito as a War Criminal to save 150,000 lives seems like a pretty fair trade-off.
There were internal disagreements among the Japanese on what conditions would be acceptable for surrender, but I believe the situation was largely that the Japanese were unwilling to accept an unconditional surrender and the Allies were unwilling to accept a conditional one. The Allies had laid out their terms for surrender in the Potsdam Declaration, and were wary of any surrender at odds with that document. After the atomic bombings, the Emperor made a radio broadcast announcing surrender which had a profound effect on the public's willingness to stop fighting, and the unconditional surrender sought by the Allies was agreed to. The way you presented it isn't entirely accurate, as I don't believe the Japanese ever explicitly offered to surrender if Hirohito was given immunity (I could be wrong on that one) and considering that Hirohito was never actually tried for war crimes. He remained on the throne until his death in 1989.
I suggest checking out the AskHistorians FAQ - the atomic bombings and the Japanese surrender are covered in depth.