If she's willing, they sometimes take some convincing..
I highly recommend sending the wife to an all women's sailing course if she's serious about learning... There have been studies that show that many women learn better in such an environment. If not that, at least take the courses separately. The reason I say this is that in many couples, if they take the course together, one will dominate and the other will not learn as much from the course.
Totally.. There is so much to learn, read anything you can get your hands on, including BAD stuff. Even 'day sails' can go bad quickly if the weather / tide turn.
An excellent learning book is Dave Seidman's The Complete Sailor. Well written and illustrated, and covers a surprisingly wide breadth of sailing information in a relatively small book. About $16 in the bookstore.
Also don't forget the 'locals' they can be amazing sources of knowledge
Joining a local sailing club or yacht club and crewing on the round-the-buoy races can be a great way to get a lot of experience in a relatively short amount of time. You'll probably start as movable ballast, but as you crew more, you'll gain skills and move from position to position on the boat. Even if your long term goal is cruising, racing is good experience, since it can teach you a lot about maximizing or minimizing the power in the sails and proper sail trim. Maximizing the power in the sails is useful if you're a cruiser and stuck in an area with little wind. Minimizing the power in the sails is good when you're stuck in heavy winds and need to control the boat.
I agree with cardiacpaul, walking the docks can be the best way to go and I’ve had many a fun sail that way. You should however have some basic skills in case the person who takes you out isn’t all that savvy or they become incapacitated.
Taking a basic ASA 101 Learn to Sail type course moves you from being deadweight to have a solid foundation of the language and skills required to be useful as a crew member. I would highly recommend that you take at least a basic Learn to Sail type course. Also, most captains have their specific way of doing things, which may or may not be right, or safe... and if you have a good solid foundation under you, it can help keep you out of trouble.