This is the set-up I've been using lately for macro shots. A canon 350D,
Canon 70-200mm f/4.0L lens, 68mm Kenko Extension Tubes, Delta Flip Flash II flash
bracket with 18 inch arm, Canon 580EX flash with Stofen Omni-bounce diffuser,
and Canon off camera flash cord.

With the lens zoomed to 70mm, the focus distance is about 6cm. At 200mm the focus
distance is 56cm. Here's a shot of a dandelion that I was pretty happy with. It
was taken with the lens set at 70mm, it is not cropped, just resized for Pbase and
a little LAB sharpening.