Don't say need. You don't need it. You want it. If you needed it, you'd be very creative at getting it, because when humans truly need something, unless they're very screwed, they are rather good at getting it.

Now, onto your problem: What repositories do you have enabled? It's possible that version of libeet1 isn't in the stock extras repository, and you may have to enabled extras testing or extras devel (standard warnings apply) in order to get it.

Or go to the maemo.org/package interface, search for libeet1, and download the .deb of the right version manually. Then put that file on your N900, run "dpkg -i" on it as root, and then try again to install the rest of BlueMaemo.