Oh... maybe then it's "hidden"; are there little arrows at the bottom of the window where this tab should be? If yes, you're saved: these arrows are there to scroll the tabs left-right... I hope this is it now.. no laughin' this time..!
Woah... then if there's no arrows just below this up'n'down scrolling usual bar at the right of the window, maybe you've undocked the Media window.
If it's docked somewhere, you could see it at the bottom of a different window appearing as a "tab" (same as when in "usual" window). Maybe the window just at the right of this left-bottom window (same window as Video Preview) ? (look for a Media tab under your Video Preview window..?)
Maybe you could try going to View and uncheck all the windows (Explorer,VidFx,Transitions, etc...) so you can "spot" it somewhere in your GUI. Then check all the tabs you want back again if no success.
Otherwise, rebooting computer sometimes help or just closing Vegas then opening again?
It *must* be somewhere... for chri++akes!