Relax....it's easy. They will only take a credit card number for special meals like eating with Cindy at the Castle. I would guess also Hoop de Doo, the Poly luau and those kinds of special shows/meals. For all regular restaurant reservations, including character meals, they do not ask for credit card info.
You really need to have an idea of where you will be so you can easily get to your meal. For example, if you want to eat at Chef Mickey's in the Contemporary plan on the Magic Kingdom for that day (or that time of the day). This way you can monorail, or walk, over to the Contemporary. Same holds true for all the MK resorts. Basically, do not just make reservations without knowing where you will be. We did that on our first family trip and learned the hard way. If you want to eat at the 50's Prime Time plan on the Disney Stuidios. You don't want to be running around wasting time travelling to eat your meals. Schedule your meals around your theme park visits. There are Guest Relations in all the parks that can help you with dining cancellations or changes to your reservations. Although it is certainly a good idea to call and cancel, if you really get stuck someplace and can't make your reservations and cannot find Guest Relations... don't worry about it. Your reservation will just cancel if you don't show up within a certain amount of time. You really should call and cancel so someone else can get in. But in extreme cases sometimes this is not possible.
I suggest you go over to allearsnet.com and check out all the great info they have on WDW. They also have all the restaurant menus available.