Take a good look, and if your source offers the 20D as a kit with the Canon EF-S 17-85mm, what is the actual cost of the lens? I would suspect it is a very reasonable amount, and I would also suggest it will provide a lot more performance than you might imagine.

When the original Rebel came out I got the kit, and did a test on a tripod using the 18-55mm EF-S for that model against a Canon L wide angle zoom with a slightly shorter range, one of the best lenses in my arsenal on film, and there was no appreciable difference in the Rebel files between the two lenses in any dimension of image quality.

Both the 17-85 and the Tamron are very nice lenses. You might also consider the Sigma 24-70 f2.8, which is a tack sharp lens, or the Sigma 24-60 f2.8 which is just as good and much lighter.
As for a 70-200, I would reccommend the Canon 70-200 f4L, which can be had used for under $500 on the for sale forums of boards like this one or Fred Miranda's.