and I've changed the type of my grids from TDBGrid to TMyDBGrid.
Everything compiles OK.
But when I run it I get Class "TDBGrid" not found.
[ I ] didn't know how to change it [...]to modify the lfm by hand in the IDE, right-click in the form and select "View source (.lfm)"; it'll open the LFM text in an editor window, where you can change whatever you want ... but you must know what you're doing!