I agree with YorkieLover. You need to make sure that this dog is wanted by your entire family, and you need to think about whether you really want the responsibility of having to feed, groom, walk, and train a dog every day. My first dog was originally adopted for my sister who was at the time thirteen (as old as I am now). She had begged for a dog for years, and while my parents had allowed her to have other pets, they hadn't yet allowed a dog. Finally they told her she could have a dog. She was responsible for training the dog (which she did quite well), walking it every day, feeding it every day, and bathing it when needed. But if she couldn't do these things, such as if she were sick, my parents would do it. They also took care of vet bills and such.
Now it is my repsonsibility to care for our first dog, and the two others we added in the last couple of years. Every day I have to get up, let them outside and refill their water bowl. I let them back inside, grab some breakfast, and start school. Throughout the day I let them out and pet them when I can. After school I walk them all (which takes me about two hours), feed them (takes five minutes to prepare their food, then I have to wash their bowls which takes about five minutes). They aren't groomed or trained every single day, but most days I'll go outside and review their commands, and work on new ones. They also get brushed probably at least once a week. A yorkie or other long-haired breed will need more grooming than a short-haired breed to make sure the fur doesn't tangle. A yorkie would also need professional grooming visits every two to three months. You can have a yorkie clipped if you don't want to deal with so much grooming.
As I said earlier though, you should go with a heavier, sturdier breed.
Here's some info on different breeds and such
http://dogbreedinfo.com/ready.htm
http://dogbreedinfo.com/yorkshireterrier.htm
http://dogbreedinfo.com/pug.htm
http://dogbreedinfo.com/englishcocker.htm
http://dogbreedinfo.com/americancocker.htm
