[jQuery] UI replacing background image after resizing, how??

[webmas...@terradon.nl]

Hi all,
i have a resizable (grid 50) div with a background image.

When i resize, i want to change my background image, like:
bg400.png for bg350.png.


But how do i detect the new heigth/width and how do i replace the
background image?


Thanks in advance for any answer!