Unfortunately dead pixels are common on TFT screens as they are often developed during the manufacturing stage. For retail costs to be kept low the companies cannot afford to make all screens defect-free and check for dead pixels all the time. Pixels can either be described as dead (permanently black) or lazy (stuck on a specific colour). They very rarely develop during use, unless you have a habit of poking the screen. If you are careful with the screen, hopefully you shouldn't develop any further pixel problems.
To test for dead pixels, there is "Dead Pixel Buddy" available program. You can manually cycle through 5 full screen colours (black/white/red/green/blue) to check for dead or lazy pixels (use UP key) or rapidly cycle through all of the colours automatically to try and coax lazy sub-pixels back to life. Leave it running for half an hour, if you're lucky it can work! (SPACE key). ESC key ot exit.
If you want to ensure that you receive a pixel perfect screen (and who wouldn't at the kind of prices you are paying for the TFT!?!) then you can often pay for pixel checks from some online retailers. Beware though! Never buy a TFT from retailers who offer the pixel check without having the check done as you can be sure the screens they find to be non-perfect will be winging their way to the customers who don't have the check! The only other option to insure you get a pixel perfect screen is to check out the panel in a shop in person, then you can see for yourself.
If you find you have a dead pixel there is not a lot you can do unfortunately. If you have a certain number of dead pixels (usually at least 3 or a certain number centrally on the panel) then the manufacturer will replace the TFT for you, but the number of dead pixels needed before this happens varies between each manufacturer, so check with them before you order if you're concerned.
Some lazy pixels can be bought back to life occasionally. Playing some fast paced games for a while, and massaging the pixel area with a lint free cloth can sometimes help revive the lazy pixel, but not in all cases. Also a light flicking with the finger has helped revive lazy pixels for some people, so certainly worth a try.
If you still have a dead pixel problem, can't bring it back to life and can't RMA it under warranty then you can sometimes return it to the stockist if you purchased it online. If you bought online you can take advantage of the "Distance Selling Act" which entitles you to return any item within 7 days as you were not present at the time of purchase. If you are not happy with your TFT you can return it at your cost of postage and often claim a refund or exchange. However, be aware that a lot of places will try and charge you restocking fees and they will almost certainly specify the goods must be packaged and in the same condition as when you received it, so be careful to package it back up nicely. Legally, if the stocker accepts the TFT back as a return governed by the Distance Selling Act, then they are NOT allowed to charge you a restocking fee as covered in the Governement Regulations (page 11 in particular). This selling act is not qidely known by retailers, but does exist if you really need to use it. You should only have to pay for postage to send it back to them.
For some good info on various manufacturers policies, and a good read about dead pixels, check here on BeHardware (updated March 2005)