I might need Weight Watcher

It’s about The 3rd tutorial of the book Bounce, Tumble and Splash which is about making a Blender floating flag.
The user have to weigh the plane in 5 different weight but how to get a straight zoning like the one which is shown in the captur ?
With the circle brush it’s never well spanned, the colors blend and I get an irregular weighing.

If it’s any help, you can select vertices and assign a specific weight to them in edit mode using the buttons under the Vertex Groups Panel. The other thing would be to make sure you’re in wireframe view in weight paint- so you can see the vertices properly- and use a brush set with strength 100% and be careful to only hit one vertex at a time.

You can make a gradient like that super easy using the ALT key while brushing.

Or, if you want more selective control. Under Stroke, choose Line for the Stroke Method. Voila, you can now weight-paint straight lines!

Stroke Method as well as your advice with the Alt key must be a feature of >2.6. It’s a tutorial for 2.49 which interface is less fullfledge (though it’s greatly enough).
What I actually need is to learn how to use the Weight Gradient plug in.

I made a few tries but had no resuts.
Click at start, at the end then the brush appears but not my gradient.
I can’t find video tutorial on YouTube nor written one on Google that treat this particular plug in.