I've already converted the files into .wav, but they're so damn big, how does I reduce file?

Bring up the .wav file in sound recorder (Start<All Programs<Accessories<Entertainment<Sound Recorder) by going to Files and selecting the .wav file. After this go to Files and then go to "Properties". Select it and then hit "Convert Now". It should bring you to a screen with many different scroll-down sections. Go to the one labeled "Attributes" and choose a smaller kHz. Also, make sure it's on "Mono" as stereo requires 2x the space. Besides, it's a map, no one needs surround sound. Also, you should be warned that reducing the size also reduces the quality, and makes it sound really bad sometimes.

I'm pretty sure there's a more sound-preserving way with Audacity.. D:

No, actually, not really, it's a pretty straightforward process, although I remember a topic a while back that Heinermann made about hex editing them for compression, IIRC, it ended up being smaller than just using Sound Recorder, however, other than that, Sound Recorder is about as good as it gets

The smallest compressed size(in general) for StarCraft is 16 bit mono(frequency decides quality, smaller size=lower quality).

16 bit 8000Hz will result in 128 kbps, and probably compressed to ~50 kbps. 8kHz is VERY muddy, though. I use audacity and set the bits in the preferences, and the frequency in the bottom left.