Por aqui fiz o código abaixo (no arquivo DPR), que atendeu bem as minhas necessidades:
var
sModo : string;
begin
GetParamByKey('modo',sModo,'desktop');
if (AnsiLowerCase(sModo) = 'desktop') then
begin
Forms.Application.Initialize;
Forms.Application.MainFormOnTaskbar := True;
Forms.Application.Title := 'G!Guadian Master';
Forms.Application.CreateForm(TfModoDesktop, fModoDesktop);
Forms.Application.Run;
end else
begin
if not SvcMgr.Application.DelayInitialize or SvcMgr.Application.Installing then
SvcMgr.Application.Initialize;
SvcMgr.Application.CreateForm(TGGuadianMaster, GGuadianMaster);
SvcMgr.Application.Run;
end;
end.