I have seen something like that before from someone here on the HLP forums though. No matter what they did, installing/uninstalling, making sure the old 1.0 dlls were gone, etc., would get it working for them. The only suggestion I had left was to recommend that they copy the openal32.dll and wrap_oal.dll files from their system32 directory directly into the game directory. And that worked. That is probably the next fix you can offer, but it should always be considered a last resort.
That proceedure isn't recommended in general, since you miss out on better OpenAL drivers which sound card makers can put out (particularly Creative, they have full hardware acceleration for their popular cards). But, it's something particular to some systems, and I don't really know what that is. I have pretty much put that into the back of my mind though, since I'm rewriting the sound code for 3.7. After that, OpenAL will be required to get sound, but won't be required for the game to actually work.