If like dancing, you will likely have a lot of fun with ballroom. You previous dance experience will be put to good use.
You should be able to find a list of local dance studios through your Yellow Pages. Take some time to visit several to get a feel the each studio's environment. Some studio's focus more on competition, and less on the social side and vice versa.
Group classes are a good way to learn basic steps for all the various dances for a low cost. I always recommend that people start there to see if they are going to like it. It also gives you an opportunity to meet other dancers. Private lessons are essential if you want to compete or if you want to advance more quickly. I personally like to a combination of both groups and privates.
A word of caution, dancing is addictive and unscrupulous studios use this knowledge to get students to spend more than they can afford on dancing. Some studios use high pressure sales tactics to sign students to expensive contracts. Make sure that you have a predetermined budget for this before you visit studios.
Blair