Windows 7 has a dedicated tool for capturing screenshots called the Snipping Tool. It can be found in the Accessories menu and it lets you capture a particular area of the desktop. Run the application and drag a box around the area you want to capture. After the capture is complete, you can use a pen or a highlighter to mark important areas on the screen. This is much quicker way of doing things than the traditional way which included capturing a window and then cropping the area in an image editor.