The defender signed a one-year deal at the weekend after rejecting an offer to remain at the Gunners.
Gallas, 33, said: "Finishing fourth last season shows Spurs have improved a lot and I hope this season we are going to finish even higher, maybe even win the Premier League.
"We just have to believe in ourselves. We have got young players with great quality, they just have to believe in their capacity to do something and I hope we can achieve this."
Gallas, who will stay at White Hart Lane for another 12 months if he plays enough games, assured fans there are no split loyalties following his four-year spell at Spurs' bitter rivals.
He added: "It was not an easy decision but I am here now and I will give my best. "What is most important to me is to play games and to give everything. "I just want to be fit as soon as possible, train with my team-mates and play matches. I want to show everybody I am still here."
Gallas trained on his own with fitness chief Sam Erith yesterday and boss Harry Redknapp expects his new signing to take a fortnight to get match-fit.
The Frenchman is confident he will be playing in the Champions League group stage as Spurs bid to over-turn a 3-2 deficit against Swiss side Young Boys at White Hart Lane tomorrow.
Gallas, who also spent five years at Chelsea, said: "Spurs are ready for the Champions League, even though they lost the first game. The team showed character to come back.
"I am confident we will win that game because all the players know it is very important to play in the Champions League.
"It is the best level to play at - you can show how good you are. "The atmosphere is so great. When you hear the music, you just want to get on the pitch and battle for 90 minutes and it would be good for Spurs."
will he be crying on the pitch again if Spurs crash at the first hurdle?
hit ur head again while shaving????