Here's how I do it in elements 6:

As MD says create a duplicate layer first, select layer-duplicate layer and make sure this is highlighted in layer box.

1: Use the quick selection tool to select the part you wanna keep colour

2: Switch to quick selection brush and change to mask, which is a selection along the line from the brush size. That colours the area's of the pic you haven't selected red so you can fine tune the selection. Make sure you have add to selection on, the left hand corner at the top near your brush info.

3: When you're happy click on select and then inverse

4: Then select enhance-adjust colour-hue saturation and move the slider so you can de saturate as much or as little as you like.

5: Job done