Tools Needed :
GIMP
Sony's Official Custom Theme Converter
PNGtoPTF

Wee'll Be Using This Icon:


1.First You Need To Make Sure You Are Always On RGB Mode : Image>Mode>RGB
   Don't Save The PNG In Indexed Mode Or It Will Come Out Messed Up When You Transfer It To The PSP


2.Then You Need To Add A Alpha Layer, To Add A Alpha Layer Go To : Layer>Transperancy>Add Alpha Channel
   If It Already Has A Alpha Channel Just Skip To The Next Step


3.Next You Select The Fuzzy Select Magic Wand Tool And And Click On A White spot On The Image And Hit The Delete    
   Key Or Edit > Clear


4.Now You Resize The Icon To 48x48. To Do That Go To Image>Scale And When The Box Shows Up Put In 48 For
   Width And Height.


5.Now You Drop The Opacity To 50% And To Do This Go To Dialogs>Layers And Set It To 50%.


6.Now You Save As .PNG And If You Get A Message Box About Merging Visible Layers Click Export And Save It With
   Default .PNG Options.


7.Now Wee Need To Convert The Icon To 256 colors 8-bit format So Run The Program PNGtoPTF And Open p The Icon You
   Just Edited And Click The Convert Button


8.Once Your Done With That Open Up The Custom Theme Converter And Click On The Tab First Level Icons And  
   Pick Any Icon And Click On Edit And When A Window Pops Up Asking For Icon Body And Icon Focus Select The Icon You
   Just Created And Press OK


9.Fill Out The Rest Of The Other Icons And Once You Are Done Select File>Export To Create A PTF

10.Copy Your Them Over To (You Drive Letter)\PSP\Theme You'll Notice A Ghostly Icon With A Ghostly Glow And
    You Are Done :D

Rules To Remember Of Sony's Thmem Converter :
Wallpaper
Wallpaper: 480x272 24-bit *.bmp

Category Icons
Icon Body: 64X48 256 colors *.png

First Level Icons
Icon Body: 48x48 256 colors *.png
Icon Focus: 64x64 256 colors *.png

Second Level Icons
Icon Body: 32x32 256 colors *.png
Icon Focus: 48x48 256 colors *.png

Others
Preview Icon: 16x16 256 colors *.png
Preview Image: 300x170 24-bit *.bmp


Icon Body: what the icon looks like when you are not selecting it.
Icon Focus: This image will appear behind the Icon Body and fade in and out when selected,


Do not use pure white (255 255 255) or pure black (0 0 0) colors in any of your images. Theme Converter may freeze if you do.

Added Pictures To Make Everything Easier :D

I used to use gimp until I got photoshop :d

Anyway nice tut!!