On the island...
The "Curly-haired Guy" is a nickname given to one of the passengers who sat in the tail section of Oceanic Flight 815. The Tail Section tore off and crashed on a different side of the Island than the plane's middle section. This group of survivors, who became known as the "Tailies", were the first to be attacked by the Others.
In their first night on the Island, three of the tailies were kidnapped by the Others. The "Curly-haired Guy" was among these three tailies. Although he was not specifically identified in any scene, he was later mentioned by Nathan in dialog:
From The Other 48 Days transcript
Nathan [entering]: Look, 3 of the people are missing—the blond guy, the curly-haired guy, and the German who was helping us with the injured.
Ana Lucia: Did you see anything?
Nathan: No, I didn't.