the biggest difference between the 20D/30D and the 350XT
is the body, which is made of magnesium alloy instead of PLASTIC.
and the 20/30D has a MUCH better grip
it has bigger viewfinder
click here
http://www.bobatkins.com/photography...viewfinder.gif
and i think another very important difference is the SPOT meter on the 30D.
image quality itself should be identical (at least very close to)
the 30D probably has more AF zones, faster AF,
maybe a bit more responsive? more FPS too? (3 vs 5)
ALSO,
i use the rebel XT too.
and i think the price difference does NOT used to justify getting a 20D over an XT,
because for the differnce in price u can almost get the 17-40mm f4
but these days the 20D got much cheaper,
so its different.