Defender Ridgewell made the switch from Villa Park to St Andrews three years ago and immediately became a supporters' favourite.
Now former England Under-21 player Gardner has signed a four-and-a-half-year deal with the Blues through to the summer of 2014, although he is not eligible for Wednesday's Barclays Premier League clash at Chelsea.
Ridgewell said: "Are there problems switching from Aston Villa? To be honest, with me, everyone has been quite good about it. I'm a London boy and everyone knew that when I came across.
"I've spoken to Villa fans when I've been out and they understood that I moved for football reasons and I think the Blues fans have seen the way I've gone about my game playing for Birmingham and there's been no problems.
"I wasn't the first to move to Birmingham and I think, if you go about it in the right way, the fans respect that.
"I remember when I came here one of the masseurs told me that as long as you give everything, tackle people and are committed, the fans would love you.
"If Craig does that and plays well every week, then I'm sure they will love him here."
Ridgewell has played a significant part in City putting together a 15-match run but knows Chelsea will provide a massive threat to ending that sequence.
He said: "It's a big test. We're all looking forward to it playing against all those stars. We've got to give them respect - but they've got to give us respect too as we're undefeated for so long and playing well.
"With any luck, hopefully we will stay unbeaten. It's a difficult task to go down to Chelsea and beat them but we will give it a good go."
Birmingham boss Alex McLeish admits he is also targeting a striker and a wide midfield player before the transfer window closes.
He is interested in signing Spurs striker Roman Pavlyuchenko and Liverpool forward Ryan Babel.
McLeish said: "Are any other deals close to being completed? There is nothing close but we are trying a couple of things.
"With the Craig Gardner move going through, we have spent a good part of £3million, a long way short of the £20-40 million that was bandied about (following the takeover by Carson Yeung).
"I have no intention of spending that amount with the way this team has played.
"But I still believe we have to spend some more money to bring in a striker and a wide man for more cover in the squad before the window closes."
McLeish is under no illusions about the task facing his City against Carlo Ancelotti's team, but believes they can play with no fear after their recent run and encouraging performances against the other Premier League big guns.
He said: "We won't be favourites to win this one. Chelsea are in great form as well and I believes they are the team to beat for the title, although Manchester United always come strong in the second half of the season.
"But we've gone to Old Trafford, the Emirates, White Hart Lane, Anfield, Goodison Park and, although we may have not taken a lot of points at those places, we've given good performances.
"We didn't look as if we were out of our depth in any shape or form and it has given the players great confidence and belief in themselves.
"The evidence is there of us going away to these grounds and being able to stand up to the task."