I think in the beginning of the game, Vergil is on Dante's side and helps him out, but later goes with Mundus and says that he was a double agent and that the reason their mother is dead is because Vergil rated his family out for power, like his father. But after their mom died, Vergil was cheated and never got that power. Dante doesn't know this and therefore, not hate him yet. By the end of the game, Vergil betrays Mundus, saying "I'll be taking what belongs to me!" Which is the power he wanted from Mundus after his mother's death. After the defeat of Mundus, Dante and Vergil go their seperate ways, distant from each other after Dante found out why their mom is dead, and the two can never be brothers again.
(Guess this belongs in the DmC theories thread but it's Vergil talk)
Now about his look, I think of him as a man in a black suit with a blue tie, a black trench coat over his shoulder (Like a Mafia boss) his hair brushed back and he'd kind of look like a mafia boss from the Godfather. His Yamato would look like a normal katana with the handle being almost like the Highlander katana and the blade being the same as it was in DMC.
That's my two cents in this Vergil in DmC talk.