You can put other ads on the page, as long as they're not contextual. I'm not sure if Adbrite is or not though.
adbrite is ok on my website, I asked google for that. I think you should ask google. some of adbrite is contextual network also, i think.
Yes, anything problems better ask google. Like mattmdesign said, anothers contextual or PPC ads can't put in sames page with adsense. For example, if you sell text link using Text Link Ads, you can put together with adsense adv.
The only restrictions Google has regarding other advertising is basically: 1) It can't be contextual 2) It shouldn't mimic or look like Adsense ads 3) Shouldn't cotain nudity, etc.