You mean like the ones in my avatar?
1. Shape tool-> rounded rectangle
2. click the paths tab, click the arrow, make selection. feather: 0 anti alias: yes
3. Fill it with a gradient as mentioned in this tutorial.
4. Copy the layer. Edit->Flip vertical
5. ctrl or apple T
6. you should see dots like this on the top toolbar:
[][][]
[]
[][]
[][][]
click the middle dot of the bottom row.
The dots will now look like this:
[][][]
[][][]
[]
[][]
7. make the "Y" textbox the height of the image. that will make the rectangle exactly at the bottom
8. Make a rectangle that overlaps the rounded rectangles so it looks like my avatar
9. stroke it, then fill it.
Also, on the rectangle shapes, you might want to add a stroke. Edit->Stroke.