Maybe it was not the ring that corrupted him but the thought of what he percieved could be done with the ring and his desire to help his people becuase unlike Denethor I think that Boromir wanted to help his people and he thought the One Ring could do it.....I think that in the end he dies with honor but I think that his need for the ring or the power that he thought that he could get from it was too overwhelming for Boromir so he did what he did.
Indeed, Boromir wanted to save his people. As an apt warrior, he must've understood that against the armies of Mordor no victory was possible, unless the Ring would be used... that's why he wants the Ring to be used. Boromir never understood why the Ring had to be destroyed... as he saw it as the only victory and only ways of survival for his people (exactly what his father thought). At the moment he spoke in the Council of Elrond, men of his city were fighting against Mordor, including his brother, and were in dire need.
This thoughts must've crossed his mind from the very moment the Fellowship left Rivendell. The Ring was able to 'corrupt' Boromir by using Boromir's will to use the Ring : the Ring turned Boromir's will to use the Ring into desire for the Ring. Perhaps in the beginning Boromir just wanted the Ring to give to his father, but due to the influence of the Ring he had visions of himself becoming a great warlord, assembling everyone under his banner and defeating Sauron.
Probably he had visions of him becoming King as well... subconsciously, Boromir always had a hidden desire to be a King... as in the appendices we can read that he once asked Denethor why he wasn't a King or how long it would be until the ppl would consider him to be a King.
So the Ring was able to get into Boromir's mind because of Boromir's will to save his people by means of arms -even though this is impossible- and changed this will into selfish desire. Unlike Faramir, Boromir never understood that the Ring was as evil as Sauron.
Give up the Halfring, she-elf...