Hi Shevvy,
I'm having the exact same problem; no voices or sound effects in starcraft brood wars, just background music. The only odd thing about my situation is that the voices and sound effects did originally work! But then one day, like any other day, I went to play some online multiplayer with a friend over battlenet, and poof! the only sound which could be heard was the background music.
I tried a bunch of the usuals: sound options, reinstalled the game, reinstalled the
drivers for my sound card, tried some blizzard support-- nothing seemed to help.
The only major change that I've made to my computer recently, that I think may have occurred around the same time as the sfx issue, was that I installed an additional hard drive, the one containing my previous os-- it has xp professional media center edition on it, along with all of the games, pictures, and music which I had on my computer before. Including starcraft.
I had planned on wiping the old drive once I had pulled off the files which I wanted to put on my windows 7 drive. I haven't finished it yet though, but I'm working on it now, now that I have some free time. I'm hoping that once I wipe the old drive and/or remove it from my system, the starcraft sfx might magically decide to work again. I haven't a clue what the connection is though. I'm only slightly techy and it's about the best thing I can come up with right now.
Perhaps you have a similar issue, in any case good luck!
I'll post back here if I manage to fix the issue.
SS