It might help to look at the manual. I don't know exactly what you want, but I'll tell you several ways to cover this.

1) If want you want is your animated logos to play when you first put the disc in the player, prior to showing the menus, then what you want is called, "introductory media". This is accomplished by looking at the top of the project overview window (far left pane). At the top there are several buttons. Go to the 4th from the left. It has a symbol of a cross on the lower left hand side of the button next to a square on the upper right. Click on this. This will open up a browser and allow you to put whatever media you want there. It will play prior to the showing of the first menu, and then automatically start playing the main menu, when that piece of media is finished.

2) If you want the actual animated logos to "overlay" or play on top of your menus, there are 2 ways you can do it. First you can right click anywhere on the menu workspace and click on "Insert media". This will overlay whatever piece of media on the spot where your cursor resides. You can also create a composite image inside of Vegas and use this as your background image. If you go to the far right on the "Menu Page Properties", there is a spot for "background media" where you can designate, via browsing whatever piece of media you choose.

There are lots and lots of ways to accomplish what you want, just be creative!