
first, open up your image in psp, or you can do this with an existing image. go to the palettes where you select foreground and background colors, and choose pattern from the first box:

click on the box that displays what color/texture/etc you have set as foreground/background to bring up your materials window. from the dropdown menu, you can choose which pattern you'd like:

I'm going to use bright emerald, it comes free with most versions of psp.
from there, you'll notice it's just like other brushes that use color, except instead, your pattern will show up: