1) Create a new image 700x400 px with a white background.

2) Create a new layer(layer1). Now use the rectangular marquee to create the size tab you want, Fill it with your desired color. Deselect (CTRL +D) now near the bottom of your tab draw another rectangle slightly longer either side to create a weird shape like shows opposite.

3) Add a new layer(layer2) and fill with black.

5) Now deselect (CTRL +D) and then go to Filter>Blur>Guassian Blur and enter a setting of about 3.7.

6) Next go to Image>adjust>levels and drag the two triangles to the center so you get a smooth shape and click ok

7) Now hold CTRL and click on "RGB" .

8) Then go back to the layers palette. Create a new layer (btn-layer) and fill the selection with your desired color.Then if you want you can apply the stroke(edit > stroke).

9) Now you don't need layer1 and layer2.You can hide/delete the layer1 & layer2.

10) Next duplicate the new shape(btn-layer) by dragging it to the "new layer" button.

11) Select the move tool and move the btn-layer copy to right and align them all up in a row as shown below.keep duplicating until you have your required number of buttons.

If you don't apply stroke in step8 your image looks something like below.

12) Now create a new layer at the top of the layers palette, now using the rectangular marquee draw a rectangle all the way across the lower parts of your tabs like show in the image, once done fill the selection in with the DARKER COLOR it will look something like I have opposite.

13) Now if you want you can add special effects to the buttons.