Here's a tutorial for making transparent backgrounds in gimp. I found this very useful.
Also to make just a part of the image transparent, you can select it and hit delete on your keyboard. But don't save as .jpg, becuase that can't support transparency, save as .png, or .tga instead.
There is an easier, much simpler way to create a transparent background in the Gimp than the tutorial shows. Open the gimp and then open your image. Click on layers-transparency-add alpha channel. Now all you have to do is is take your wand and select the section(s) that you want to be transparent and click edit and then cut. There ya go short and simple.
Love will humiliate you and hate will cradle you.
Jealousy would be far less torturous if we understood that love is a passion entirely unrelated to our merits.