once an image is burned in - it's burned in. I have a samsung 52" plasma and have never had any problems with it (yet). usually an images gets burned in after a day or so, not after 5 minutes.
Return the plasma, it's obviously got some big problems.
Dunno about getting a LED-LCD, i have one of those too (also samsung), it's good but the plasma is better. This is a strictly personal opinion though.