How to change the resoultion of machine

[MITTAL Pradeep Kumar]

Hello,
 
Is there any way so that one can change the resolution of the machine to
800 * 600 by using some rev function ?
And then after reset the resolution to the previous settings.
 
And the same thing, I would like to do for sounds. Is there any way to
control the volume ?
 
Thanks for your help.
 
Best Regards
Pradeep