J.D.
L.,
First, Congratulations on your family's new addition! My youngest brother is adopted through the foster care system as well, and I remember how excited we all were at the time.
Your son is very lucky to have such a great playmate! One of the great things about adopting an older child is that he and your other son can bond so quickly, and not have to wait years of growing up time to have it be fun to have him around.
As far as how they play, that's pretty much what boys do. They run, jump, fight, and yell. If you wanted quiet and civilized, you needed to sign up for girls. :) You can set ground rules to control it somewhat, no jumping on furniture, no hitting each other with things, etc. It's not going to work real well, but you can try. Your best bet is really as much outside play time as possible. Have whoever takes care of them in the afternoons take them out. Let them run and jump and climb and yell, wrestle in the grass, kick a ball around, duel with sticks, etc. They need to do this stuff. They just HAVE to. It's part of a little boy's nature. It'll make it easier to enforce inside rules if they have an outlet for these activities.
I know I'm the biggest chicken-Mommy in the world, and cringe every time I let my kid loose on the playground, so it's silly that I'm the one giving this advice, but relax. They're going to fall down, they're going to get bruised and cut and scraped. It's another facet of a little boy's nature. If you've got a six year old in the summertime with intact skin on his knees, someone is doing something wrong. Stock up on Band-Aids, antiseptic, and popsicles. They're going to fall off their bikes and bump heads running after the same thing, and all that stuff. There's no real way around it.
If you think about it, do you really want there to be? Six years old is one of the all-time great ages. There's an incredible joy to just being that gets lost so quickly, and the freedom to just do stuff because it's fun is a window that closes fast. As long as they're not on the top bunk, let 'em jump on the bed and hit each other with pillows. If they fall off, kiss their boo-boo and give them a cookie. It'll be so soon when that won't work anymore. And someday the won't be six, they'll be twenty-six, and the furniture won't have scuffs and stains, and the house will be quiet again. No one will be crashing cars all day. What a damn depressing thought...