Heres another modeling option using Bryce terrains:

Open Bryce, from the create panel select a terrain model. While the terrain is still selected:

1.-Ctrl+E brings you to the terrain editor.
2.-Make the terrain 512 pixel resolution and make sure solid is disabled by clicking on the down arrow at the top of the terrain canvas.
3.-In editing tools panel, click down arrow next to the fractal button and choose rounded dunes for your terrain type.
4.-click the fractal button until you get a terrain that satisfies you.
5.-Back in the editing tools panel, drag the raise/low option to the right until the terrain in the 3D preview just lightly shows the terrain.
6.-Accept the terrain, this brings you back to the main display.
7.-Using the resize button, elongate along the z axis the length you want.
8.- Also in the resize button, elongate along the y axis to add more pronounced fold to your rug.
9.-Add your texture and your rug is done.