If I’m understanding correctly what you want to do:
Draw your path.
Select your Brush tool.
Set the brush the way you want it (size/shape/color).
In the Path palette, select the path and click the Stroke Path with Brush button at the bottom (the hollow circle).
That should stroke your path with the selected brush.
If you have Illustrator, you can do basically the same thing but with a lot more flexibility, especially if you want to go back and edit the path or brush later.
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It is easier to destroy than to create.
More fun, too.