Do you have experience shooting candid people photos? Sports, news, anything? If you can do those things, then you have some of the skill set required for shooting a wedding. I'm a news/magazine photographer, and end up saying "yes" to this sort of thing about once every five years. The results are usually decent, though afterwards I swear I will never shoot another wedding.... They are very, very hard work, and six or eight hours of humping heavy gear in a hurry with the added pressure that you can't really miss any of the photos, well, that's why good wedding photography costs a lot of money.
I shot my most recent wedding in December. Dark church, of course, with mixed fluorescent and incandescent lights. But the minister gave me free rein during the ceremony, as long as I could shoot without a flash, and I took advantage of it. High ISO with your 5D2 is very good -- don't be afraid to use it. If you want to add some fill flash, make sure you gel the flash to match the color of the ambient light (this is easy if it's an outdoor wedding during the day.) Talk with the bride and her mother well before the wedding to make sure you know every shot they want, and also to make sure that they understand your particular photography style. For example, if you are a fine art landscape photographer who shoots everything at f/64 on a 4x5 camera, that might have an effect on how you cover their wedding
. Look at good wedding photo sites (start here
. Page down for some great wedding photos.)
Just btw, depending on how ancient your Speedlight is, it might not work with the 5D2.
Good luck. The bungee jumping accident might start looking pretty good at some point....