Now, Mike has a 04 ram, which has a different headlight setup than mine from the sounds of it.
I preheat my oven to 225, if your nervous about ruining anything, 210 will actually do the trick as well. Same as Mike did, 20 minutes in should soften that glue up enough for you to pull it apart.
On my headlight, I tried to use a screwdriver, and it actually bent up the plastic in a few places, try to just separate any type of snaps there may be with the screwdriver, and the rest should be pulled apart by hand. If it doesn't come, don't force it, another 10 minutes in the oven, and kick up the temp 10 degrees to soften it up again.
By the way, wear some mechanics gloves, 225 will heat up the light enough were it'll suck to touch it.
When putting it back together, I normally put the back of the light into the oven for about 15-20 on 200 to soften the glue up again. Put the light back together, and use whatever clamps necassary to hold the light together.
The clamps Mike listed may work on his, but for my light setup, I don't think they would've been successful. I used a longer adjustable clamp, and had to try and push the back of the light into the front lens, the edges weren't really an option on mine.
Mine didn't seal back up on the original glue, I actually bought 2 tubes of Black RTV sealant (4 bucks a tube at your local Wal-Mart) and used a tube per headlight putting a nice bead around the edges, with the light together. This should be done when you are happy with the project, and pretty much know your not gonna bake them apart again. The RTV is best when you let it sit for at least 16 hours, but I recommend 24 hours if you can. The RTV may not look real pretty, but you won't be able to see it from anywhere unless you take the headlight apart, so nothing really to worry about.