Install this:
http://www.codesector.com/audiosliders.php
have it replace Windows Volume Control.
caveat: I've never used this software for a Media center edition of WinXP, I'm not sure what affects on Media Center specific software it will have.
If you tell me the exact make and model number of your laptop, and the make and model number of your sound card (if you have a separate sound card, I can point you toward a 2nd option that is a proper solution that I found when I had this problem.
Everest says the sound card is a SigmaTel Audio and it's onboard.
Then under "PCI/PnP Audio" there's an "Intel 82801fb ICH6 - High Definition Audio Controller [B-2]" listed.
The motherboard is a Intel Pentium 4 521, 2800 Mhz (14 x200).
[see, I write this like I actually know what all of this means! I'm a GEEK!]
Thanks for your help...
Very cool. Thanks.