That other interiors thread really doesn't have much of the info your looking for. Realistically shooting outside is going to be your best bet to get some great interior shots. I normally like to shoot in the shade while still making sure their is plenty of ambient light. A nice, wide, fast lens like a 24mm on a full frame body or an 18 on crop should allow you to get the whole interior from the right angle and then I always like having something with a zoom (normally my 70-200) to get detail shots of cool things on the dash etc.
As far as shooting interiors when inside, I generally will use a softbox containing a 5 CFL head shining through the opposite window of the side I am shooting on. I'll usually roll the window down so the glass doesn't refract the light and kind of make it glare (even though I am probably shooting with a CPL filter anyway). For darker interiors I will use 2 soft boxes, one on either side of the car. The single softbox tends to give a shadowy look but that is usually the style I am going for anyway.
Heres a shot using one softbox on the opposite side of where I am shooting...

It's dark and shadowey but again thats the look I like.
I believe this one was two soft boxes on either side of the car with the one on the left slightly lower power just to fill in a little...