The ebuild for ymessenger asks for ymessenger_0.99.19-1.tar.gz, which I am supposed to download from http://messenger.yahoo.com/messenger/download/unix.html. He specifies "Note that you need the one for Debian Sid", but the one for debian sid is ymessenger_0.99.19-1_i386.deb.
No, it's not. Look at that page carefully.