The EOS 40D with 28-135IS USM is indeed a very good bargain if you need the 28-135IS lens. The one probelm is that 28mm isn't very wide on an EOS 40D. It's equivalent to a 45mm lens on a full frame camera, i.e. a "normal" lens. This means that the 28-135 isn't a perfect "walking around" lens where you're likely to want a wideangle. It's a very good lens and the 28-135 range (45-216mm full frame equaivalent) can indeed be very useful.
I am new to digital SLRs. I have the 28-135IS that I used on a film camera. I don't understand the talk about the full frame equivalent. What does it mean? Will my 28-135 be useful on a Rebel XTi?