Fixed positioning only until a certain point

[suavedesign]

I have an element (a nav bar) on my website that has fixed positioning. How can I make it be fixed only up to a certain point?
The url: http://www.peresidences.com/index.php
I want the nav bar to be fixed positioning only until it reaches under the picture, and then it should stay where it is, and not come down further.
How can I do that???
Thanks...

Second reply on http://stackoverflow.com/questions/5902822/stopping-fixed-position-scrolling-at-a-certain-point looks promising

GIY: "fixed element position stop scrolling after point"

[suavedesign]

thanks, I did find that, and I followed that script, but I came up with an issue:
http://www.peresidences.com/index2.php
The nav bar now scrolls until a certain point, like i wanted it to, but instead of staying put when i tell it to stop, it jumps to the bottom of the screen.