The source doesn't work for people in a newbie slap. It's best to use code snips.
[ code ]
Your code here.
[ /code ]
Just remove the spaces between the brakets and it'll do this:
This sounds kinda weird. Sprites naturally replace the background as they move... unless the default setting for the sprite is changed with the "set sprite" command. Without seeing code it's hard to say what's going on.
To get a sprites background to be transparent use black as the background and don't use .jpg... jpgs change the colors... use .bmp.