I think 'pixeled' borders make the whole graphic look better instead of a just plain line. Pixeled Borders are something that look like THIS
After you have made your graphic go to Image --> Add Borders on the PSP toolbar. It should look something like THIS make sure your size is 1 for all of them.
Now do the same thing 2 more times with a lighter color, then another lighter color.
Once you have done that do it one more time with your beginning color!
To make the finishing pixel touch use the color white, and the square paint brush (size 1) and draw a few white squares around the second border like THIS