Banks make it sound hard to open a business account without being incorporated, but it isn't. You just tell them to set it up as either a sole proprietorship (one sig) or partnership (multiple sigs) and you use your SSN(s). The organization's name goes on it as DBA (doing business as) but you should check beforehand to make sure it isn't being used, just in case you wanted to call yourselves McDonald's or Chrysler or something...
The only downside is that you and your partners are liable financially for everything, including back taxes and penalties should the authorities decide there is any money to be had out of you. And they can get quite creative and nasty, even when you think there's nothing in it.
The IRS came down very hard on banks in the US about 15 years ago, and now they are all quite anal about having all the tax identification info correct, to prove they aren't helping you launder money for terrorists or Nigerian diplomats.
-Glenn