TUTORIAL: Using Various Graphics Programs to Make Drapes and Folds.

3D Programs
1) Daz 3D: Making clothing folds on a specific folds
2) Creating Fabric Drapes in Bryce

Paint Shop Pro
1) PSP Drapes
2) MardiWeb Drapes in PSP
3) Tephras Bishop Sleeve Drapes
4) PSP Mesh Warp Drapery
5) Using PSP Mesh Warp to make a Drapery Swag
6) CSGreen PSP Drapes
7) CSGreen PSP Drapes #2

Photoshop
1) Drapes in Photoshp 5
2) Abduzeedo: Surprise behind the curtain in Photoshop
3) How to create shimmering floating soap bubble and curtain drawing effect using Photoshop
4) Photoshop Tutorial - Fabric Folds

Additionally;
Robin Wood: Adding Patterns to Cloth using Photoshop (scroll down)