Take a look at the sticky thread at the top that may be your problem if i'm understanding your question.
If you are Creating your own menu using FullCanvas then just use drawstring to draw your lable (i.e. select) over the softkey then listen for the softkeys button being pressed. (you can find what it is if you check the java docs that are in the Nokia folder if you have the Nokia Suite installed.)
As for unloading things from memory set them equal to null.
Image ball = createimage("/image.png");
//when you are finshed with the image
ball = null;
System.gc(); // call garbage collector