new photographer with flash question

Hello!
i am wondering, when using a flash (420 ex w/canon digital rebel) can you use any ISO and get good pictures? is this normal practice.

i am new at this taking photographs under pressure (not just hobby!) and i am wondering if i set the ISO to 400 lets say, in a darker room setting, will i still get a good shot?

Yes - the flash will adjust to the ISO you set. In dar rooms, I routinely shoot flash with my camera set at ISO 800 (and even 1600) to capture as much of the ambient backbround light as possible.

That's really an important point - if you want to include some of the ambient background, you need to set your shutter speed/ISO/f-stop separately from the flash in order to pick up that ambient light while getting just the right flash exposure or affect you are after on the main subject....