Image swap Help

[ctechguy]

I have a top frame with thumbnails and a lower frame name ="main" where i want the image to enlarge.

<a href="#" onMouseDown="MM_swapImage('main','','large pic address',0)"><img src="thumbnail pic address" name="Image1" width="130" height="97" border="0">

I left out my address for security reasons

Main is also the pic i'm replacing

How do i tell it what frame the pic to replace is:?