Try this, it might help.
First remove your sound card drivers via Programs and Features in the control panel (if there is such an entry). Let the computer reboot and if it asks after rebooting to install drivers, cancel it!
If after rebooting, it installs some drivers without asking you, then OK, just go to Device manger.
In device manager, right click your sound card and click on uninstall AND check the box "Delete the driver software for this device".
After that, just reboot and when Windows asks you for your drivers, cancel it and install the very latest Vista sound drivers available for your laptop.
Again, remember that it has to be Vista drivers and as latest as you can get!
As per your post, you said that you have an AC97 on board sound chip. I found the latest official Vista drivers for them from Realtek here: Realtek
But, these drivers are generic; meaning that if HP's drivers give you some special functionality, chances are that these drivers won't give you that functionality. Hence, I urge you to first check with HP's suport if they have latest Vista drivers for your laptop available and use those first!
If they don't work, you may try Realtek's drivers.
Hope this helps!
Thank you for your time!