Many Windows media players use DirectShow to play videos. So, to play a video/song/whatever, you need the appropriate DirectShow decoder. VLC includes it's own codecs, so missing DirectShow codecs aren't a problem.
Here are names and descriptions of some useful DirectShow software.
ffdshow is a DirectShow decoder that covers most video and audio formats, but it won't take advantage of the Broadcom card.
CoreAVC is a commercial codec for h.264/AVC video. It's generally lauded as the better performing than ffdshow's h.264/AVC decoder, but it costs money.
Haali's media splitter takes a file and splits it into the component video and audio streams. You'll need it if you want to play .mkv files.
VSFilter enables you to view softsubs. You might not need this.
"Codec packs" generally package up some/all of the above software and more into a single install, but I'd rather just install the bare minimum, from the real sites.
As for performance, you shouldn't need the Broadcom card to play DVD resolution videos. But the Broadcom card may help with low-res YouTube vids, though, since Adobe Flash sucks at playing videos. I don't know if the Broadcom card will help older formats like DivX or Xvid. It's mostly intended for h.264/AVC video at HD resolution.
I also think the newest version of VLC for Windows can take advantage of DXVA (DirectX Video Acceleration). I hope/expect this enables it to take advantage of the Broadcom card.
Feel free to ask any followup questions.