The required resources for ShowDialog XCMD to function are:
XCMD 2155 "ShowDialog" (you can renumber this XCMD if you wish)
and then whatever DLOG/DITL/ICON/PICT/cicn resources that you construct with ResEdit.
Use the DLOG/DITL resources in this stack if you don't want to make your own. The cicn resources in this stack are OPTIONAL. If you have a color monitor, the cicn (for color icon) will be displayed in place of an ICON of the same ID number. This is no big deal but my feeling is that any way I can squeeze some color into HyperCard is worth the effort. If you don't have a color monitor this resource type is ignored (so they don't hurt).
The "icon bar" dialogs look especially nice when cicn's are used.
Trouble Shooting: ShowDialog provides a full range of error messages. If one of your parameters is incorrect, ShowDialog will exit with a beep. If this happens try putting "the result" into the message box. The result should contain an error message that is indicative of the mistake.