I installed Delphi 7 on Windows 7 x64. Things went well for while, but now, when I open or create a data module it messes up the component palette. By messes up, I mean it seems to scramble which tabs components are on, or hide them altogether. This is really unusual behaviour.
Uninstalling and reinstalling Delphi 7 hasn't helped.
The component palette is context sensitive, so that tabs that can't be used aren't displayed. (Visual components make no sense in a datamodule, because you can't put a visual component on a datamodule. There's no point in showing you components you can't use.) A tab that has only visual components on it will be totally hidden; if there is a mix of visual and non-visual components (like the Win32 tab), only the non-visual components will be displayed.
Switching to the design window for a form should display both visual and non-visual components, including making those hidden tabs visible again.