Actually, if you're using a tripod, a lower ISO and longer exposure times will yield a better photo. But not so slow a shutter that you have to worry about tracking. Higher ISO will also mean more "noise" in the image. A remote shutter release is preferable, if not, use the timer to avoid camera shake during the shutter press. Your Canon (assuming EOS line) has a setting for mirror lockup. That will help reduce shake as well.
As stated, you're using digital, so clear out you CF card, read up on your camera setting, and plan out what you want to do exposure wise and go wild. Try all sorts of settings. It's not like you have to take film in for processing.
What lens(es) are you using? Have any filters or lens hoods?
I have a Canon Rebel XT and an Olympus Evolt 500. Evolt has a 14-45mm 1: 3.5-5.6 lens. The Canon has a EFS 18-55mm lens.