How to take photos in the dark with a nikon d5000?

I'm going to be taking pictures at a party and they will be only diso lights on so it will be kinda dark so how can a take pictures in low light with a nikon d5000

1) use a hotshoe flash like the SB-600 or
2)Bump up the ISO, get a monopod, and use a fast lens with a f/1.4 or f/1.8 aperture

You have a few choices-
Use a high ISO though this will make images grainy.
Use a fast lens for example a lens that lets you use an aperature of F1.4 -F2.8.
Use a slow shutter speed though everyone will be blurred but it'd make interesting shot's.
Use your pop up flash or a separate flash gun like the sb800.
Finally you should shoot in RAW which means you can make them brighter in Photoshop later and the images won't suffer as much as they would if they were taken in jpegs.