Need a few quick tips before wedding tomorrow!

I know I shouldn't have left this until the last minute, but I am a DSLR newbie and I have a wedding tomorrow. Fortunately, my friends have hired a "real" photographer and I am not being paid. I still want to do the best that I can though...

My questions:

1) I've read that the white wedding gown and veil will cause a lot of problems with autofocussing. Any tips to get around this? Also, how do people get the pictures of the detail in the dress?

2) The church is a pretty small one, and flash is allowed. Any suggestions on how to use the Flip-it effectively? Also any general overall tips? I will be using my Sigma 18-50 f2.8 HSM the most I think.

3) Following the ceremony will be pictures at a park. The time will be around 4:30 to 5:30 (sunset here is around 7:30 right now). Any tips on making the best use of the natural lighting?

I have the D40 and the following lenses: Sigma 18-50mm f2.8 HSM, kit 18-55mm, 18-135mm, 50-200mm VR.