netscape layers problem

hi
i just have a problem with the netscape layers.
i tried to have an image switch (for a button) and a text, which gets
displayed by
a netscape layer over the button!
well. i tried it, but i didn't got it yet.
i used a <ILAYER> to get the position of the button (for the layer)
-----------
Can any1 of you explain me, why it is not working,
that i can NOT access the source of the image?

here is the code which i used:

<ILAYER width=128 height=96 name="erst">
<LAYER name="ha" width=128 height=96>
<TABLE width=128 height=96><TR>
<TD align=middle align=center>Hi</TD></TR></TABLE>
</LAYER>
<IMG SRC="button1.jpg" name="haha">
</ILAYER>


now, how can i access the source of the image)?
i tried it by (javascript):
document.images[0].src
document.haha.src
document.erst.haha.src,
but no one worked!
hope you can i help me.
thanks a LOT, if you want to help and try this problem.
cya
patrick