calculate percentage of parent DIV

Hello,

So I am having trouble with my slideshow script!

This is the code:
Code:
$(document).ready(function()
{
$("#showcase").awShowcase(
{
content_width: 640,
content_height: 480,
}
)
This decides my slideshow images width and height. Is there a way that I can tell my script to use a certain percentage and not pixels as a measure?

Because I want my gallery width and height to be in percentage so it will automatically adjust regarding of the parent DIV width and height (parent div is in percentage as well)

Can somebody help me out please?

Thank you in advance

Luka

P.S.

This is the website where the slideshow is:
http://vertel.info/myprojects/larie1

You can see the parent div (with red border)....