This thread is misleading, because that package in getdeb-page is NOT Debian 64 -package. That package is not compiled for the 64bit Debian. It's compiled for the Ubuntu. Ubuntu is not Debian even if it's based on Debian. You should never install packages which are not compiled for the distro you use.
If you use Debian Lenny (current testing) then you can install glest from official Debian repository. Glest packages are currently available for the alpha, amd64, arm, i386, ia64 and mipsel. You can install Glest this way:
# apt-get install glest
I use Debian Etch (current stable) and I would like to see glest packages for it too.