You can speed up the Vista Windows Mail program by disabling the splash screen that is shown every time the program starts. To get rid of the splash screen, open the registry editor (by running the regedit program). Once it opens, navigate to HKEY_CURRENT_USER + Software + Microsoft + Windows Mail on the left side.

Once you get there, look for an entry on the right side called NoSplash. If you have it, click on it to change the value to 1.

If you don't already have this entry, right click on right side and select New -> DWORD Value. Name the new value NoSplash and give it a value of 1.

Once you then close the registry editor, you will no longer get a splash screen when you start Windows Mail.