Would you care to tell me some about the metering on the A300?
Sure...here's the very basics:
If you go to 'P' mode, which will be the same as it was on your H2...that will give you basically auto everything, but with the ability to make some settings changes to customize a bit.
The first adjustment is the ISO - but you found that one. It is obvious!
The second adjustment would be the EV, or exposure value, which you can adjust up or down by a stop or two. This is a small button on the back top of the camera with a +/- on it. If you press and hold this button, and turn the thumbwheel, you will see the EV scale on the LCD screen showing your adjustments into the '+' or '-'. This will let you selectively increase or decrease the sensitivity as needed.
The third adjustment is the Program Shift. This won't change the exposure of the shot, but it will change the shutter and aperture combo used to get the shot. If you half-press and get a shutter of 1/1000 and an aperture of F3.5 for a properly exposed scene...you can adjust the P Shift by simply rotating the front thumbwheel (on the screen you'll see a little '*' next to the P), and the camera will hold the exposure, but adjust the aperture smaller and the shutter slower, each counteracting the other by the same number of stops. In other words, if the aperture goes to 4, the shutter will drop to 1/500 in order to hold the same exposure. This allows you to ensure you get a faster shutter speed if you need it, or control a shallower or deeper depth of field as needed.
The next adjustment is a bigger one - the Fn button just above the 4-way selector pad on the back. This Fn button will pull up a 6-button grid on your LCD screen, allowing you to use the 4-way joystick pad to move around to any of the 6 selections, and press the center button to adjust that setting. Your choices are: Flash Mode, Autofocus Mode, White Balance, Metering Mode, AF Area Mode, and D-Range Optimizer. Flash mode is where you can adjust for slow synch, red eye, etc. Autofocus mode is where you can choose Continuous, Single focus, or Auto (chooses between the two as needed). White balance is the same as on your H2. Metering mode allows you to choose Multi-segment, Spot, or Center weighted metering. AF Area mode allows you to chooce multi-segment focus area, wide focus area, or center weighted focus area. D-range optimizer you don't need to worry about - it adjusts minor sensitivity to dynamic range with regard to shadows in high contrast scenes.
This is all easier than it looks - the little 4-way controller can be scrolled up, down, left or right to the 6 choices, then the center button clicked to enter that mode. Once entered, your choices will pop up on screen, where you just scroll down and select what you want (similar to the H2). Pressing the Fn button, Menu button, or half-pressing the shutter, will all pop you out of this menu and back to ready to shoot.
The Menu button is something you really only need to enter when you are changing camera set up - such as the resolution mode (10mp, 7mp, 5mp, etc) you are shooting in, whether you prefer RAW or JPG shooting, and adjusting the creative styles like sharpness, contrast, color, and saturation if you find the photos need more or less of one of those things.
That should get you off the ground. As you grow more confident, you can start using A or S priority modes, and just use the thumbwheel at the front to set the shutter or aperture as needed depending on what priority mode you are in...the camera will select the other parameter, focus, and ISO unless you tell it otherwise.
In M mode, the only thing you need to know is how to adjust both the Aperture and the Shutter, since there is only one thumbwheel for both settings. This is pretty easy too - one of these two will be adjusted by simply turning the front jog wheel - usually Shutter speed is the default. In order to adjust the Aperture instead, you press and hold the '+/-' button and scroll the front jog wheel. This will now be adjusting the aperture. The scroll wheel on front controls both shutter and aperture - one by pressing no other buttons, and the other by holding down the +/- button.
Hope all that helps!