I'm looking for a tutorial to create wavy flowing threads. Like this:
I'm open to tutorials in Photoshop, GIMP, or any freeware image manipulation program. We have a copy of PS. I'm not sure if another graphic app is in the budget.
I'd use Inkscape's calligraphy tool to draw the curve, if I were you. It's way easier, and more powerful than anything you'd get with GIMP/Photoshop.
If you really have to use GIMP:
You can use curves (somewhere in the toolbox). Draw a curve (preferably without anti-aliasing). Make the thickness something large enough. Now, select the curve using the Magic Wand/Floodfill tool (possibly by selecting the background, then inverting selection?). Next, use a gradient (not sure where it is - I use Paint.NET mostly), and overwrite the curve with your gradient. Later, you can add highlights using more layers (create layer, same process, but make the gradients smaller.
EDIT: A little tutorial I made, as requested. Be sure to read the captions for instructions!