Please try to create a test page from scratch without any of your stuff and just put the HTML I gave you.
You can see it on a test site I use here
Link removed (no longer valid)
If you resize the browser, you will see the Text column gets bigger but the image always fill up to the bottom of the text columns. Let me know if that is what you were after.
What weaver refered to is something that is different and probably wont do what you want if what I have above is, but once you have seen the test page and let us know we can discuss more