what you most likely have is "image retention" rather than burn in. you can clear this up relatively easily. more on that later.

now, while i won't deny that burn in still exists, plasmas are much better at resisting burn-in nowadays. but you should still take care of your screen.

first off, turn off that godforsaken "vivid" mode that the tv is set on fresh from the factory. then break in your tv - turn down contrast and brightness quite a bit, and watch it that way for AT LEAST 100 hours, on fullscreen mode (no black bars on the sides). you're more likely to get burn in/image retention early on in the tv's life since the phosphors are so new. you want to "age" the phosphors evenly at first, so when you get back to regular viewing the image retention isn't as noticeable.

you can get through the 100 break-in hours pretty quickly by burning and running a "break-in dvd" found here:

http://www.eaprogramming.com/downloads/downloads.htm

it's basically a full screen of colors that switch over time. i popped this in my dvd player and let it run overnight. you can also use this to get rid of the image retention that you currently see.

after that break-in period, bump the contrast and brightness to your liking (use AVIA or DVD Essentials to get correct color/brightness/contrast etc.) and watch whatever you want, however you want without fear.

btw - i'm posting this from my plasma right now, and the white okayplayer screens doesn't cause burn-in on my screen even after an hour of surfing. hope that puts you at ease.

for some recommended reading, visit this forum:
http://www.avsforum.com/avs-vb/showthread.php?t=608677

you can probably find a thread specific to your model of tv.

enjoy your plasma!