To get optical stabilizer or not / Rebel XT or XTi

My sister is looking to either get a Canon Rebel XT or XTi coupled with a Sigma 18-200 mm lens either w/ or w/out optical stabilizer.

Realizing of course that XTi w/ optical stabilizer lens would be the nicest, her budget is not unlimited.

Would be grateful for recommendations if/why the XTi is worth it over the XT, and whether to splurge on the optical stabilizer.

Thank you.

I have an XTI and love it. I believe that the XTI has a built in sensor cleaner, and the XT does not. For the price difference, I went with the XTI

I wont comment on the camera body because I am a Nikon shooter but as far as the IS(image stabilizer) goes its almost useless for sports shooting. The purpose of the IS is to compensate for camera shake at slower shutter speeds which can be the equivelent to a couple stops of light, but this does not mean it adds a couple stops of light. with sport shooting you will 99% of the time be using faster shutter speeds and so camera shake does not play a large role in the image quality and so the only way to really get more light to your camera when shooting sports is to have a faster lens. If you are buying the lens as your "everything" lens and will be using it for indoor portraits or anything that isn't sport shooting and can use slower shutter speeds then by all means get the IS lens. I have one and in low light it works great but like i mentioned it really doesnt contribute much to sport shooting. i hope this helps.

Awesome, thanks. That is very helpful.