Can someone pease remind me how to disable the Windows Defender splash screen that runs when the pc starts. I still want Windows Defender to run at start but want to stop it opening. Did it before but cannot recall or find how.

In my opinion the best way is to use Microsoft Security Essentials as your antivirus. Defender is part of MSE, will be part of startup but no splash screen. In addition, you will have one of the best anti virus protection for Vista.
I use MSE in conjunction with a malwarebytes scan once a week.