Unlock Shane McMahon and Stephanie McMahon Helmsley
To do this you need to unlock all the smackdown cards. If you have unlocked all the above then go through one of them again to get to Wrestlemania. You will unlock about 3 to 4 cards each time. Another way to do it is to defend a belt. Each time you defend you unlock a card. However when there are three cards left (Shane and Stephanie's cards included) you will need to go through story mode and win WWF title at Wrestlemania. Choose anyone who doesn't hold a title.
Tell Vince you don't want to form a Tag Team.
Talk trash.
Say you want to kick his ass.
Go to parking lot to find Vince.
Win match.
Show up on stage.
Win match.
Win match at Wrestlemania.