I've seen floating menus on several websites lately that llok like a menu bar on the left side of the screen. If you scroll down on the website, the menu scrolls down as well, so it retains its position not on the website, but on the monitor. When you mouse over it, it expands.

I'm pretty sure I can figure out the expanding part, but how do you keep the menu's position on the monitor?

An example of what I'm after can be seen at http://www.youthpastor.com.