multiple blogs, one user database?

i have a couple of WordPress blogs hosted at my website, FlyerFlies.com, and everything has worked out rather well for me. the only thing i would like to change is the fact that everytime i create a new blog, i have to copy the entire user database table over from one of the existing blogs. and then, that only adds the people that are registered on the existing blog. it still forces people to register for a user account for each blog separately.

what i would like to do is have it set up where one user database covers each of the blogs. if you register for one, youre automatically registered for all of them.

is there an effective yet easy way to do this?

thanks.