To get the shot you are looking for a filter is used to reduce the light input. This goes for any camera, F8 on a small lens is only a pin hole, same as f22 on a larger lens, so no problem with your cam only doing F8.

Set your ISO manually to as low as it goes - less sensitive to light.
I don't know the camera so first thing to check is does it have a built in ND filter? Some Canon cameras do, find it in the menu or manual. Use this to reduce light it could be all you need.
Alternative is a separate filter that either screws onto the front or has some kind of adaptor so that you can fit it. There are methods of fitting them to all cameras though you may have to search for it.
The filter you need will reduce light input.
A polarising filter reduces light by 2 stops or there are neutral density (ND) filters that reduce it by more if needed. They will say when you look at them how many stops lower you will get by fitting the filter.
Shots of water falls etc are usually best taken on overcast days so the range of light from the brightest to the darkest is at its least.
Hope this helps
Richard.

Message edited on: 03/31/2006 06:30

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html