Stop the table header from scrolling?

I have a scrollable table javascript that I am using. I would like to know how I can keep the header from scrolling out of view. I would like to make it fixed. How can I do this??
Thanks

 

Can you post a sample code or point me to the page where you have this scrollable table?

 

A sample of the code would be helpful but what you will most likely need to end up doing is playing with the positioning of the header using CSS. So say your header is called #header. You would add the style
#header{
position:absolute;
top:0;
left:0;
}
This will take the header out of the normal flow of the webpage and force it to always be on the top left.
You can make this relative to the rest of your site like force it to be in the top of a 'wrapper'... this is where seeing your actual site/code would be extremely helpful.
Also, I recommend checking out this quick tutorial about using CSS positioning