Since you can get Debian for the PPC, I would guess there are many packages that should install onto YDL using Alien. However, you must ensure that they are either source files or PPC binaries. It should go without saying that binaries for any other architecture than PPC will not work on PPC machines.
ftp://ftp.se.debian.org/debian/dists/Debian3.0r2/ seems like a good place. Just browse to the powerpc sub dirs for the debian files you need.