I think the PP's have given you some great advice.

I think being a great birthing partner is about a whole lot more than just what happens on the day. It's also about preparing for the big day together. I'm not sure how much research your DW is doing to prepare herself... I know for me, I did a lot of reading and my DH happily read what I read and we put together 'our' birth plan together. It was as much his as it was mine. Yes I was the one who was going to be labouring, but it was about the birth of 'our' baby. We discussed the different area's at length and really went into the experience with a shared mind set if that makes sense.

If you are interested in a great book for you both to read that will help you both prep for the big day and give you a real idea of what to expect, New Active Birth is fantastic. Before reading it, all I knew was the hollywoodisation of birth - waters break, then you're in hospital on your back screaming while you push. This takes you through the entire process, educates you about pain relief options and most importantly positions for labouring in (if you ask me it's essential for your birth partner to be familiar with the positions, because when you're in the moment you may forget).

HTH and GL!