Save the image to another user's texture folder
Go to the folder Local Disk (C > Games > Toribash > customs > pick whatever user you want to save your left bicep to (ex: hampa) the item format should be .tga, save, then open toribash, lp hampa
There are lots of items of all sorts in Toribash and it is almost impossible to obtain all of them.
However, you can try them on in the ingame Torishop by pressing the "TRY" button next to each item. This can both help you to choose the best color combination for your Tori and make you familiar with different item types (it's always easier to see them instead of reading plain text, isn't it?).