the first step is to get the cat to the vet to be sure there are no health problems.
If all is clear on the health front, then the problem is behavioral. You will need to take steps to retrain the cat to the box. Basically this involves isolating the cat in a small room with the litterbox, water, food and bedding and waiting until the cat uses the litterbox consistantly before allow her to have access to the house.
Also ask yourself if anything has changed around the house. Sometimes even small changes like moving furniture around can upset a cat to the point where he/she develops problems using the litterbox.
You need to thoroughly deodorize wherever the cat has been peeing. Nature's Miracle is highly recommended and is available at most pet supply stores. It is the smell of the "accidents" that causes a cat to reuse the place or clothing.
Check into using Feliway, a spray that mimics the happy scent cats leave when they rub their check against something. You can read about this at
http://www.feliway.com
Finally, if all else fails, ask you vet about using an antianxiety medication such as Buspar or Prozac. These very often work, however the decision to prescribe them will rest solely with your veterinarian who will be able to monitor the dosage and side effects.
