Sigh... First test before committing. InvalWindowRect and friends are window object methods. Fixed.
diff --git a/Mac/Tools/IDE/Splash.py b/Mac/Tools/IDE/Splash.py
index 1544b67..b71e0ca 100644
--- a/Mac/Tools/IDE/Splash.py
+++ b/Mac/Tools/IDE/Splash.py
@@ -100,7 +100,7 @@
 	if drawdialog:
 		splash.DrawDialog()
 	drawtext(what)
-	Win.ValidWindowRect(splash.GetWindowPort().portRect)
+	splash.GetDialogWindow().ValidWindowRect(splash.GetDialogPort().portRect)
 
 def drawtext(what = 0):
 	Qd.SetPort(splash)