First, create a new image, 250x100 pixels and fill the background with the color that you like.
Use Custom Shape Tool [U] to draw a shape that you want your button to look like.
Now is the time to add Inner Shadow to your shape. Right click on the text layer and select Blending Options...
Layer Style window will open, select the settings that you see on the screenshot.
In the Layer Style window select Inner Glow on the left and use settings that you see on the screenshot.
In the Layer Style window select Bevel and Emboss on the left and use settings that you see on the screenshot.
In the Layer Style window select Contour on the left and use settings that you see on the screenshot.
Press ok when you done and your image should look like mine.
Congratulations, now you know how to create Mac OS-type buttons in Photoshop.
