Yes you can place adsense and adbrite together on a same website, I would suggest you to go with Adsense ad units, link units and search box. And you can use adbrite's intext ads and full page ads, otherwise there will be too many adblocks on the same page, so users will get fed up with that..!
you are allowed to add both the things together as long as you use different colors for them.. i mean that, they must look different.. " ads by google" "ads by adbrite"
yes u can but i do not suggest u do that coz comparin adsense and adbrite is a joke. if adsense pays u .50$ per click adbrite will pay .01$ for the same , so why u wana divert ur adsense click to ur adbrite ? keep usin adsense and do change the ad placement once in a while for sometime then stick to the one which gets u more clicks, blend ur ads with ur site and its color.
We can put both the ads, but as compared to adsense , adbrite ads gets less click. Adbrite shows full page ads, intext links, and images as there ads.
yes you can, but i do not recommend, i had that on my website, if you use the option on adbrite to replace in case they have nothing, they will just "steal" your best visitors ( US , UK) , and on the crappy traffic they display adsense. mixing both individualy? adsense pays better to me.