I haven't even heard of the Rebel XS and based on the way the buttons are placed it seems to just have a smaller body.
I hadn't heard of it either so I had a punt round. The Digital Rebel XS is the latest entry-level model in the Canon DSLR range. It's known as the EOS 1000D in Europe &
"inherits features from both the more expensive EOS 450D and the older EOS 400D cameras. It has an almost identical body and control layout to its bigger brother, the EOS450d, whilst sharing the same 10.1 megapixel CMOS sensor, 2.5 inch LCD screen and 3.0fps continuous shooting mode (in JPEG) as the EOS 400D."The different numbers are confusing but I copied the above from the review here.
http://www.photographyblog.com/reviews_canon_eos_1000d.phpHere's a cross-reference.
EOS 350D = Digital Rebel XT
EOS 400D = Digital Rebel XTi
EOS 450D = Digital Rebel XSi
EOS 1000D = Digital Rebel XS
I think I would look around for an XTi. You should be able to get one at a reasonable price with all these new & untried cameras on the market.