Yes you can but make sure both dont look a like. Also running both ads together will have a disadvantage because adsense pays far more than adbrite and the visitors to your site will have choice either to click an adsense ad or adbrite which will decrease CTR. But if you only have adsense, visitors will have no choice but to click on adsense ads only. Got my point
you can, yes. adbrite earnings are really low though. i gave adbrite several tries until abandoned them.
Of course you can, nothing against it in Google's TOS. I wouldn't recommend even running AdBrite unless you're getting tons of pageviews, though, as their CPM is really low and you need to be hitting xx,xxx or xxx,xxx ad views daily to really make something.
Same here, I was getting 1 cent clicks. You can run them both but they must look different, as stated all ready here.
yes, you can. Only, they don't need to look the same. To avoid little payment from adbrite, you can set adbrite to display your adsense code untill they'll have better ads to display on your site. They(AdBrite) have an option for you to set a minim limit for ads displayed, otherwise they'll show adsense ads.