I would like to find the values of some of windows API constants, such as, but not limited to LVM_ENABLEGROUPVIEW & WM_SHOWWINDOW
Looking on the n
Most of them can be found in the VCL source, primarily in the Windows.pas file. Your best bet is to do a Search|Find In Files, type the name of the constant you want to find the value for, set the Search Directories option, set the file mask to *.pas, and enter the path to the folder containing Windows.pas. The IDE will find all uses of the constant and put them in a Search Results window; double-clicking on the source line in that window will open the file at that line.
Others can, as Kevin and GameCat mentioned, can be found in the header (.h) files in the Windows SDK, downloadable from MSDN.