I draw on PSP. ^_^ One of the most important things is to use layers. I usually do my preliminary sketch on the bottom layer using the Paint tool on 1px. Make sure it's a light color so that you won't get confused when you do the lineart. Next I create a layer ontop of the sketch and use the Bezier Curve on black for making smooth lines. The size of the brush really depends on how big your picture is; I usually use 1 or 2px. After the lineart, you can erase the sketch and create another layer, putting it behind the lineart layer. Now, I usually do all my base color on one layer, and then make separate layers for my shadowing and highlights, using the Multiply and Screen options. PolyKarbon has a great tutorial on this (
link!)
Unfortunately I don't have much experience in downloading or creating brushes; I've always used what's already on the program. But here are two great PSP7 tips/tricks/tutorial sites:
ZimmerTech
Andrew's Resource Center
One more thing, you should probably draw larger than you actually intend the picture to be. It's easier to line and color that way, and you can get in more detail.