The npower Championship side are aiming to cap a miserable week for Villa, who were humiliated in the Capital One Cup semi-final by Bradford on Tuesday night, by knocking them out of the FA Cup.
But Jackett said: "In a cup tie like this we are the underdog. Up until recently their results had been very good, but lately the confidence seems to have gone out of the team. Maybe that's what you get with young players.
"But even if Villa were mid-table they would still see this as a tricky tie. Our responsibility is to put on a performance that justifies that and can lead a passionate crowd towards a good evening."
Captain Danny Shittu is in his second spell with Millwall and has first-hand experience of facing the hostile Den crowd as a member of the opposition.
"If the fans can get into them the way they got to me when I came back with QPR, I'm sure it will affect one or two of their players," he said.
"As a player, we try to block it out and it is hard.
"This would be the last place I'd want to come after a loss to Bradford."