First let me clarify that you're using MSP 8, on a Win7 computer?
In the preferences dialog (File menu>Preferences or pressing [F6] on you keyboard) you set the default duration. This is found on the General tab toward the bottom Default inserted clip duration, and is the number of Frames. So I would guess yours has something like 50 frames (PAL) or for NTSC-60 frames. If you want the default duration longer, enter the number of frames or use the up/down arrows beside the entry box.
This will not affect clips already in the timeline. So you need to select all the clips in a track to change the duration of those clips..
With the Track selection tool, select the track which selects all the clips, then right-click on a clip and select Duration from the menu.
The Duration dialog will open, enter the duration. NOTE in this dialog the format is H:M:S:F (hours, minutes, seconds, frames), where in the Preferences it just allows for the number of Frames..
Ron Petersen, Web Board Administrator