Go into Quick Mask mode (down at the bottom of you toolbar, the button to the right) and select any tool, I like the paintbrush, then selest a brush size, it will put a red cover on the picture where you ask it to and then when you apply a filter or whatever, the only section that will be affected is the part colored red. Does that make sense?! It's hard to explain, but let me know if you need more info.....

 

hmm easy enough... thanks

 

ur easy