You are comparing 2 different models:
LN32A450 is 720p with a 10,000 to 1 contrast ratio.
LN32A540 is 1080p with a 10,000 to 1 contrast ratio
LN32A550 is 1080p with a 15,000 to 1 contrast ratio.
The LN32A540 is a great tv. Consider your source you will be viewing on your 32" tv also. If your watching every day tv and are or not upgrading to HD, you will be perfectly fine with the 720p model. All retail stores price match now so you can purchase it from Circuit, Best Buy, or Costco's. Best Buy and Circuit City are both doing great financing promotions this week which you may want to take advantage of.
I am buying the Samsung LN32A450 LCD based on research and CNET's review. But now I found the LN32A540 at Costco. Samsung's website shows the 540 as 1080 while Costco shows it as 720. All other specs appear to be the same. Costco sells the 540 for $799.99 while Best buy and Circuit City sell the 450 for $799.99.Is this the same tv?