Villa face United on Saturday and have previously this season beaten clubs like Chelsea and Liverpool.
Dunne said: “We know on any given day that we can beat anyone. We have got a squad full of top quality talent. Nobody should be afraid going into the game on Saturday.
“We all respect and know how good Manchester United are, but if we are to challenge the top four, these are the games we have to go and have the belief to play and impose our game on them.
“Manchester United have a decent record against Villa but this season we just feel a little bit different and we have got tools to win games against the big sides.
“We will give it a really good go and try and prove to Manchester United and the rest of the league that we are here to challenge for that top four.
“From every angle, United can attack. We just have to concentrate on ourselves and we know as a team we have to defend and when we do get opportunities, we have to take them.
“It is going to be everyone fighting for each other.”
Dunne added: “The win in the Carling Cup against Portsmouth and the win over Hull means the confidence is high but we know how tough it is going to Old Trafford.
“My record against United is not bad! I’ve had a few draws and wins but every game I’ve played against them before has been a derby. Saturday I imagine, will be a different atmosphere.
“December is a difficult month for every team with the amount of games. If you can start it well, and get points on the board, it is great and sets you up for what lies ahead.”