is it really worth buying the new 40d with a 28-135 lens?
The whole point here is, for a first time user/buyer should I just go for the Canon 40D or the nikon d80?
So, for your first question. I've used the 28-135 on a Canon DSLR for years and thought it was fine. Wider is nice, but if you don't need wide or want to shoot with a film or full frame digital camera, then the 28-135 is a nice mid-priced lens. On a 40D... eh. I'd go with something wider initially.
For the second question... for a first time DSLR buyer, I'd recommend neither of these cameras. Get the 400D or D40x kits. If you find you like using a DSLR, then invest in expensive lenses, then invest in better bodies when you need them. I didn't follow this advice when it was given to me, of course