sndvol32.exe should live in the windows\system folder.

Next thing to do is check in there and see if there is any file call sndvol32 - make sure you have set in my computer, tools, folder options, view, the ability to see hidden files and protected sysem files, also make sure you have unchecked hide extensions for known file types.
If it is not there, get your xp disk and go start, run and type in SFC /scannow and click ok. That should put it back.

Do you have service pack 1 and all updates installed for xp pro?