PC microphone

I've realised that I need a microphone, especially for left 4 dead, i.e. steam.

I was wondering what peoples thoughts were on whether to get a pc headset with one earphone so that I could still use my nice 5.1 speaker set. (like the xbox 360 one)

Or is it better to get a good 5.1 surround sound headset with 2 headphones to use for fps games?

I've been looking for an answer on this but I can't seem to find one. Most likely my failure though.