Questions about Frames and Flash

[Herrjosua]

I'm working on creating flash buttons for my website, but I am having a slight problem. All the pages except my welcome page have 4 frames. How would I create a link that would only change the bottom frame? Below I will draw a simple diagram of what my framesets look like:

Frameset1 Frameset2 Frameset 3
---------------frameset4--------------------

Thanks
Josh