Most of the advice above is good. I shoot both commercial, portrait and wedding photography, however, if you've never shot a wedding, or portraits for that matter, then taking on a wedding for the first time is an incredible undertaking and responsibility. Of course, it really depends on what the client is expecting too. If they're expecting 'snap-shots' that's one thing, but if they are expecting decent wedding photographs that could be something all together different.
I always say you need to be three things to be a wedding photographer... the technician that knows their equipment inside out and has backup equipment for when things go wrong, the artist to capture not only beautiful images, but emotional ones as well, and a psychologist to handle the stressed out bride, mothers and guests. John is right in this respect that you need to be able to communicate 'effectively' with people, usually people that you don't know, however, you also need to know how to pose or place people with a wide variety of body shapes, styles and heights in a flattering position so the groups don't look like a football team - like how to pose a tiny, petite bride beside her 250lb groom (or vice versa!).
The trend with recent wedding photography is a more casual and photojournalistic approach, however, the bride and groom are only two of the people interested in the photography. The family and guests in the parents or grand-parents generation are from a time when carefully posed and well executed portraits are preferred. And don't forget.. beauty is in the eye of the "check-book' holder! - and if the parents are footing the bill, you need to cater to their wants as well.
In summary... I would say RUN!
