I tried to find the audio spec for your machine, but none of the PDF's I looked at felt the owner might need this information - this proves them wrong.
Chances are you need drivers for both the audio processor and HP buttons that control the audio. The XP or better, the Vista drivers for your system should work with Win7. Windows 7 is mostly just Vista with some visual improvements. Most likely only 32 bit will be available, so make sure your using Win7 x86 (32 bit).
If that doesn't work, find out the audio chip manufacture and part number and go to the source, i.e. Realtek.
Also, give PC forums a try, not dive forums. The title computers is really dive computers and connecting them to computers. The PC forums will have more expert advice than a SCUBA board.