This topic is kinda old, but I'm going to weigh in anyway.
I converted some 'base' BG2 voicepacks as part of the VoxForce project back in 2002 or so. IIRC I used the 'Infinity Explorer' to extract the wav files from within the data chunks... it also works with other Infinity Engine games (IWD, IWD2, Planescape).
I think the biggest problem with BG1/2 soundsets is that there is not too much of each; basically you have several 'select' sounds, one or two 'attack' sounds, maybe a 'critical' sound, a 'wounded' and 'dead' sound, 'pick pocket', 'trap disarm', and the various generic comments when being above/below ground, happy, unhappy, etc. It's kinda hard to fill out all the possible 'sound slots' (mental blank, hypnosis, rage, etc) from there.
otoh, nwn1/2 (and now, Dragon Age) should be much more varied wrt voicepacks.
For other games with lots of potential, I suggest Wizardry 8 and Jagged Alliance 2 (two great games from a company that has sadly dissolved), and maybe the Silent Storm series... those are all tactical party-based games where having extensive (and distinct!) soundsets for all characters was a de facto requirement, and there is a LOT of them. During the VoxForce project, I only extracted about half of the Wiz8/JA2 voice files, and even that was enough material for over a hundred voicepacks.
As for conversion, Audacity is excellent. I am not sure if it has cross-file volume normalization (you might need it for less professional voicepacks where some voices are much louder than others), but DBPowerAmp used to be able to do that, and probably still can.
take care,
-- Z.
