Nope. 17mm is 17mm, but that particular lens is designed for full frame cameras like 35mm film bodies, or the 1Ds or 5D digitals. It has a larger image circle to cover the larger formats where you'll get the wider angle from, but crop body DSLRs have smaller sensors that don't see out that far.
To get the same angle of view that that 17mm lens will give on a 35mm/1Ds/5D, you'd need the EF-S 10-22mm lens which is specifically designed for the crop bodies with smaller sensors.
Your Rebel XT probably came with the EF-S 18-55mm f/3.5-5.6 lens. If it came with the excellent EF-S 17-55mm f/2.8 IS USM, you're already doing very well. Even so, there's not a lot of difference in the field of view between 17mm and 18mm.
18mm x 1.6 Field of View Crop Factor = equivalent field of view of a 28.8mm lens on a full frame sensor.
17mm x 1.6 FoVCF = 27.2mm equivalent
10mm x 1.6 FoVCF = 16mm equivalent