Excuse me, all the homework I have just finished must have exhausted me
Yes, you can lengthen those sounds. It is a registry setting that allows you to set the time you would like these sounds to play. With the ContactSoundMaxTime key you can change the value from 12 to somewhere between 1 and 100. You can use Plus! Tweak, a small program, to change your registry values easily.
Take a look at
http://www.msgplus.net/help_registry.php for more information