It's not an "hijack". If the installation of the SB software had gone correctly, you wouldn't be seeing any values in "RunOnce"--the key is used to run the final stages of an installation following a reboot and the setup program is expected to delete the values as well as temporary installation files.

Since you say it works with the drivers, uninstall the Creative software and (only if necessary) reinstall the drivers.

I'm at home on my Win98 machine so I can't speak to XP, but with 98, you enable/disable the Windows volume icon on the first page of the Control Panel Multimedia applet.