The canon EF-S system has only recently been introduced. The lens mount while looking the same is actually a little longer and so protrudes further into the camera body..this makes it incompatible with the majority of Canon camera bodies as it will foul on the mirror mechanism.
So basically your 18-55mm and EF-S 60mm F2.8 Macro USM lens will NOT work with the majority of bodies where as your EF75-300mm F/4-5.6 III USM lens (and any other EF lens) will. Canon EF lenses are by far the more popular out of the two types and have been manufactured for many many years.
EF-S lenses are not that common yet and the ranges that Canon manufacture them in is also limited. It is also worth remembering that a 350D will accept both EF-S and EF lenses though so you'll not need to worry about compatibilty on your digital body.
As long as you stick with a EF lens on virtually any Canon film body you will be fine.
Hope that helps
