1) You might already going on this path but with the current state it is strange that CheckinDialog and CheckinProjectDialog do not derived from the same VCS check in dialog class, like:
CheckinFileDialog extends CheckinDialog
CheckinProjectDialog extends CheckinDialog
Comments, focused component, additional options (missing right now see next point) could be migrated to the base class and shared.
2) CheckinDialog doesn't support additional options (CheckinEnvironmnet.getAdditionalOptionsPanel). Usually if more options/info is provided on project checkin, it would be relevant for file checkin as well. As an example we enter SCR number and pairing info. So it would be easier if both dialog would be extended the same way (see my earlier point).
3) Seems like CheckinProjectdialog uses the Dimension key of the Starteam checkin project dialog.
4) Could we talk about http://www.intellij.net/forums/thread.jsp?forum=23&thread=28445&tstart=0&trange=100 ?