I highly recommend Tailor for creating an ext3fs partition (or changing the size). I've used it successfully and it is pretty straightforward although I've mainly used the meta-doctor to create the initial ext3fs and, at the same time, bumped up the size of the /var partition.
With that said, when I first started trying out the Chroots (and pre-tailor), I just used a 2GB *.img file which can be mounted without actually creating a partition. I found it helpful to be able to configure the installation and then simply copy the *.img file to my desktop computer as a backup or base install. There are some drawbacks to doing this, including a 2GB size constraint. I'll dig up some links if your interested.
Also (I mention this because I've foolishly forgotten this step once or twice), don't forget that you have to be sure that the ext3fs partition is mounted at boot or mount it manually after each reboot.
Having forgotten to mount the partition prior to installing the Chroot from Preware, I always had to uninstall and reinstall the package from Preware.
Also, FWIW, I'm running 12.04 now, after doing a command-line update and it's great! I've found many advantages to the update. For instance, I can now use the Java browser plug-in in Chrome while, under 11.04 it wouldn't work. (Java does work in the Debian Chroot).