Running 32bit userspace under 64bit kernel:
1) First of all resize your ext3 /dev/xvda partition to free up about 2-3Gb of space for swap and recovery install. Then fdisk xvda to align first partition to filesystem size and add two more partitions: swap and rescue. Format them using mkswap and mkfs.ext3, then rsync prgmr's original Debian 64 to rescue partition. You should do above from provided Centos rescue. Youd should mount under something like /tmp/d1 because all other locations including /mnt are readonly.
2) Now format /dev/xvda, get somewhere a 32bit Debian already installed and rsync it to /dev/xvda mount point. Note: you can boot Debian32 with the kernel provided by PrGmr, so you can take it from rescue made on a previous step.
3) Boot into a newly created linux on /dev/xvda and download two files for up to date kernel:
from any debian64 repository mirror. Though arcitecture is different you can install them fine by a command like:
dpkg -i --force-all /download/*.deb
Reboot and enjoy an up to date Debian 32bit under 64 bit kernel :)