Some people may not know but it is possible to get long exposure times (up to 30 seconds) on a Nikon D70. This is done by putting the camera into 'Bulb mode' as it is called. To do this, you'll need to set the camera setting to 'manual' mode and then turn the shutter speed dial until it goes into 'bulb mode'.
Now when shooting, hold down the shutter button for as long as you want (this will be your exposure), when you release the button that is when it takes the shot. A little advise, it is often better when you have something to control the button remotely while taking the shot as this will reduce any camera shake by holding down the button for a long time.