Nightclub/Party Photography

My friend has asked me to be the photographer at her party. It will be at a beer garden, with not much natural light and more "party" lights. I've never taken photos for a party before. I'm using a Nikon D3000 and I have 3 lenses: 18-55mm, 55-200mm (both Nikon) and 8-16mm Sigma Wide Angle lens. I don't have any external flashes yet. I was wondering what type of lens I should, and what techniques would be good to use.
I've never done this type of shooting before so any advice would be helpful!

You should probably use something like a 35mm or 500mm prime lens…

or a 24-70mm

and a fast lens… F/2.8 or larger aperture…

the 18-55mm isn't good in low light…
the 55-200mm is too big and slow…
the 8-16mm is too wide for a "party"…

get a flash… And a diffuser…

This will be a dark setting. So it's likely that no fast lens will be fast enough. You really need an external flash. You'll get a lot of red eye with your camera's pop up flash, not to mention blowing through the battery before the end of the night. The 18-55 would be the proper lens. The wide angle will distort facial features. You'd have to stand outside the beer garden to get shots with the telephoto.

1- Get some fast glass like a 50mm f1.8 (or better like f1.4) or a nice 24-70 f2.8
2- Get an adjustable shoe mount flash
3- Learn how to bounce the flash off ceilings and walls and/or get a small softbox and/or bracket.
4- Shoot at a high ISO (3200 probably)
5- Shoot in RAW (.nef) so you can make slight adjustments in post processing to white balance, noise reduction and exposure.

If you can't buy any of the above, rent it.

Your camera has a built in popup flash.

Just use that.

Your existing 18-55mm will work just fine along with the flash. You don't need to buy anything extra to just take photos at a party. And your popup flash has an Auto Red-Eye Reduction mode.