Terrible....this is not only your problem
In the last days I've tryed again to install Debian,too but I've always failed.
I've tryed different installer version but all stops in different point during the base-install,the most frequently errors that I've found was "cannot find a stable kernel version" or "is not possible to install a bootloader" or something like this...
If you are more lucky than me..try to find a working installer her:
http://people.debian.org/~luther/d-i/images/
the stable version should be the 24 or 25 august one (powerpc)!