Hi there DD, i got the same cam, and trust, you can get SUPERB images.
Now all you need is some NICE glass, which makes all the differene really!
Changing iso on the XT is so simple, just press the shortcut button on the back of the camera.
You wont need to use a high iso with a good lense, unless you are doing dark/dimly lit shots, and even there is V usable. If you go into the custom functions, there is a function which will reduce the amount of grain on long exposures, but the camera will 'think' for the same lengh of time the shutter was open for.
Anyway, welcome and enjoy your stay at POTN!
K