Portrait Help

[Nitzanah]

I'm pretty new here and to photography as a whole, so sorry for any dumb questions.

Basically, right now, I have one main goal and that is to be able to take portraits of myself, spouse and kids at home so I don't have to keep paying $200-$300 for sessions at my local JC Penny or Sears for every milestone my kids reach.

I have a Nikon D40 with the 18-55mm f/3.5 - f/5.6 ED II AF-S DX Zoom-Nikkor lens
A Nikkor AF-S DX Zoom 55-200mm f/4-5.6G ED
An SB-600
and a setup like this one here

The problem I'm running into is I don't know where to start. You know, you go to Sears or Pennys and you know the photographers there have no real training or skill but they can get the photos to look right. Mine are either too dark so the white muslin looks beige or grainy or otherwise not clear.

While I do want to learn and develop a skill in doing this, right now I need to what I need, where to put the lights or if I need more/different equipment. I also need to know what mode/settings to shoot in. Any help is greatly appreciated.

[zona5101]

Biggest thing you have to battle is lighting. Sure those big box portrait employees might not know much but they have the gear and only need to follow a canned recipie.
First, forget your background. Let it go gray or beige or whatever, concentrate first on getting the light on your subject correctly. I do not know anything about those lights you have linked to but can guess they may not be all that powerful. You will probably need to move them in very close, just out of camera, to get enought light. Added bonus because big, close light is good, it wraps around better and produces smoother, more tamed shadows. If your lights do not have a way to adjust the output, you will vary the light impacting the exposure by varing the distance between the light and the subject. This will be how you control your lighting ratio between your main and fill lights. There are plenty of threads and illustrations of different light positions on the internet but you may want to try a set up where the main light is in tight and above right of your subject, your fill light will be back a few feet over a few feet to the left. (This is where moving the fill light in and out will be experimental).
You will want to have a shadow from the main light but you are going to soften it with the fill. Good luck - ask more questions.

[mitchcook]

This is worth a seriously long, and thoughtful read.
Strobist: Lighting 101
I usually play around with my camera on a tripod for a while with no one in the picture to get my settings and thoughts just right.
Toss someone in there and make sure there are no terrible shadows.
Jump in and see how the results are!
What mode do you usually shoot in?