First off, you have to have a tripod. It's almost impossible to hold a camera perfectly still, even the faintist movement will cause image blurr or visual noise. Make sure the glass is scrubbed clean both inside and outside of the tank.
I have the same camera, including the 18-55mm standard lens, I also have the 55-200mm VR and the 105mm Macro VR.
You'll have some issues using the 55-200mm lens due to focal length, it can be done, but you'll have to be about 4' away from the tank in order to focus on the subject. When I first got my rig, I had the same setup, and I used the 55-200 lens all the time, it was a pain but the images aren't bad, your just limited as this lens is not designed for this type of photography
Your better off using the 18-55mm and then the included softwear to crop and enlarge
Use MANUAL focus, autofocus sux on macro lens, just can't capture the details that a human eye can
Put the camera in "A" mode,
Set the ISO to 200 by hitting the magnifying button twice and then use the arrows to adjust
Hit the magnifying button again, then use your thumb to turn the rotating control on top right and set the fstop at to something like 16
If the photo comes out to dark or light, then use the (+/-) exposure control button to the very right of the on/off button, HOLD it down and at the same time use the thumb control dial to adjust the exposure lighter or darker and then take another photo.