You could get everyone to run fast or slow to get the effect or..... you use the Velocity envelope, right click the clip and select the option. Lift the line up or down to achieve the effect also adjust the duration of the clip to suit. You can aso double click on the lne to get handels to have more control on the velocity envelope. OR when trimming a clip if you hold the CTRL key that will spped up or slow down a clip, you shoul see a zig zag line running throgh the clip if you have done this.
See the help and the manual for more detailed infromation.
If you want precise control, you can right click on the event and select Properties. Then, change the playback rate. While you're in this dialog, you can also check "Force resample." Vegas is supposed to resample all events that have been slowed or speeded up, but this will make sure of that. Failure to resample leads to jerky results.