A couple of things -
First, I suggest plugging into a soundboard only as audio backup. Not only can things go wrong (I once had a sound tech accidentally turn on a local mic while he ate Potato chips during a wedding and chatted with his girlfriend). Another reason is that the house mics just don't do as good a job as my own mics (Shure & Sony). By using your own mics, you get to decide mic placement and you're in charge of quality.
However, if you must go with the soundboard, look for RCA jacks that say "Tape Out" or "Line Out", etc. Otherwise, you need to be aware of whether your output is preamped. For instance, you certainly wouldn't want to connect your camera audio jacks to a cable designed for speakers.
Like Tom said, a digital recorder is ideal for this - whether connecting to the soundboard or using a couple of Shure mics on mic stands, etc. I use my Marantz 660 to record 44.1k PCM wave files. This way I get CD quality audio, which is great for performers, musicians, etc. You can use cheaper digital recorders (MP3) to capture voice, if you're sure you'll get clean sound and won't have to edit the audio.
I've hooked to a lot of soundboards. I've used 1/4", RCA and mini-plug, but I don't think I've ever hooked XLR from a soundboard, so be careful! - and remember, 3-prong XLR is only one channel.