I'm thinking about an HID upgrade on my '06 from this outfit
Unique Auto Lights. They are local (to me) and I've heard good things about the product and support, although not from any Ram owners. As I understand it the kits are pretty well plug and play without having to mod the light housing. My friend has their kit on his Land Cruiser and is very happy with it.
There is no such thing as DOT approved HID headlights for any vehicle, or "DOT approval" for that matter. The DOT stamp on a product means the manufacturer is making the claim that the product is compliant with all Federal Motor Vehicle Safety Standard that apply to it. The DOT has no authority to test and approve, or disapprove, ANY product. Legality regarding HID headlights I'm sure falls under local state laws and will vary from state to state.