Will my canon EF 28-90mm 1:4 5.6 zoom lens fit a canon 350D digital camera body ?

Yes, it will work perfectly. Just keep in mind that with the 1.6 crop factor of the 350D sensor, the lens will effectively be 44.8-144mm.

Canon was smart, they built both bodies to accept all of the lenses...

Yes it will, the new EF lenses fit all the new SLR bodies

Yes!