It's a shame their budget is so low, or I'd do it
(My packages range from $3500 to $7500) But I am a professional wedding/engagement photographer, so I would listen carefully to what I say...
I don't intend this to be mean/rude, but I don't think you have any idea just how far in over your head you are.
You're capturing a once in a lifetime event, with no chance for do-overs. A lot of people say they don't care about their pictures, and then the bride is in tears days later when they see the amateur pictures and realized they messed up by not hiring a pro. It upsets me when people do this kind of thing, because they'll spend $3k on catering and $1K on flowers that will be gone and wilted by the end of the night, but they wont spend $3k on pictures that will last a lifetime, to show to their grandchildren, etc...
Your only hope is that the wedding is outside in good light, and even then, your pictures will not be near the level of a professional. You truly need experience to shoot a wedding successfully (and I mean really successfully, not OMG this pic is teh bestest! that you'll think are good) If the reception is at night or in any kind of hall, you're in so far over your head nothing will save you now. I have over $2k in lighting equipment just to take pictures in reception halls, plus the know how to use it properly.
You can use "portrait mode", but no auto mode is a substitute for manual mode. A wedding is too dynamic and changing to use anything but manual mode and you have to be fast, and you really need the full control over lighting, setting flashes manually, etc.
Kroner19 gave an excellent point about not enjoying the wedding, you're going to be so busy taking pictures that you won't get to enjoy the wedding, which you may not care about, but still.
I can guarantee it is going to be 10x harder than you think it is. There's a reason we charge such high rates, and there's a reason people pay it.
I don't have them available to post directly, but check out my website, and scroll down a little to the latest blog post with the dancing pictures. That takes years of experience and $$$ in lighting equipment to achieve. It was actually pitch black in the room, except for the LED lights on the walls. Your D5000 and tripod are woefully inadequate to get good images in a reception hall, and you don't have the experience or talent to get great wedding pictures (and running and gunning won't help either)
Again, I don't intend to be rude or condescending, I just don't think you realize the magnitude of the situation, and I think you're grossly underestimating how easy it is to get good pictures at a wedding...
Trying to instruct an amateur on wedding photography a week before a wedding is like trying to teach someone to perform surgery a week before an operation. Wedding Photographers are artists, people pay for their artistic interpretation...it's not something you get by buying a $500 camera at BestBuy, you either have it, or you don't. Hence the reason we can charge what we do.