Sticky header block module?
This is just a CSS thing!  There a tutorial here on how to achieve it, but you're pretty much just looking at some CSS like the following. 

Edit: The tutorial has now gone, but the CSS contained is very similar to that shown below, and a quick search in your favourite search engine will return similar results.

#BLOCKID {
    position: fixed;
    top: 0;
    left: 0;
    height: 160px;
}


Just apply the CSS to your chosen block and you're off.