OK, so your phone does polyphonic ringtones, not MP3.
You need something like this...
LG Data Cable
With that, you can connect your phone to your PC via a USB port, and with the correct software, upload JPG's to use as wallpapers etc.
For more info, go here...
Howard Forums - LG
With a little perseverance, you should be able to hack your phone and upload your own ringtones etc.
Hope this helps.
Heh, someone else in here reads howardforums too? Nice.