If this is RMXP, then you can do this easily with events.
All you really need to to is choose the one you want for your title screen, and select it under System tab of your Database. Your title page windowskin will be the same as the one listed here.
Then, open up the list of event commands, and you will find "Change Windowskin" on the right-hand side of the first page. All you have to do is make sure this is the first command your game runs, and your windowskin will change.