How to take good night photos with a subject?

I use Nikon d90
Tonight I'm taking night photos where there will be ambient light eg lamposts etc.
My friend is modelling for me

How do I take good night photos where there's a good balance between the subject and the lighting in the background? What settings on my DSLR should I use to ensure the background will not be too dark?

I was thinking about using rear-curtain flash but i don't know if that will be a good idea. Can someone please give me some settings i can use eg. ISO 800 etc. Thanks.

I have the kit lens and i'm not planning to use any light equipment cos i don't have any.

If you are going to take good pictures at night with a subject, I suggest you have a night mode on your camera dial. Any other mode can effect the shutter speed, aperture, ISO settings and make sure you set it that is best for the environment. I prefer using a Nikon, Canon or any camera that has more than 10 mega pixels if you want a good shot. If you need advice, ask any professional photographer and he/she can give you the best answer.

Well for a start you are now gong to have mixed white balance light sources from the street lamps (whatever colour they may be) and flash which is balanced for daylight, so that'll be a pain to sort out.

You have to think of it as 2 separate exposures - flash & ambient, so you need to expose for the ambient (which will mean long shutter speeds) and illuminate the subject with flash - use it subtlely to avoid nuking them out. Rear curtain is a good way to go, but if you rely on TTL meter you may over expsose because the camera will see a load of dark in the frame & think it needs to fire on max to light this up! Suggest spot metering on your subject. Or shoot at manual flash power levels for more subtle control.

It's sometimes best to shoot before full dark so you have some intersting colour in the sky.

This one is lit with off camera flash, dropping the ambient exposure by about a stop to get richer colours in the sky and then bringing the subject up with flash, gelled with an orangey filter to match the colour temp of the sunset;

If you do decide to get a flash -don't think you have to go Nikon brand. A cheap manual flash, radio trigger (to fire it wirelessly), light stand & umbrella/softbox will together cost around £100 - much less than a single Nikon SB600 (£220) speedlight.
Have a look here (short video a littel way down);
http://strobist.blogspot.com/2006/03/lighting-101.html