At this time those with a 64 bit processor have the option of installing the 64 bit version of Ubuntu. Not all software is available in the 64 bit environment. In particular non-free items are usually 32 bit. For example the Flash plugin is a 32 bit program.
Some programs can be run in the 64 bit version of Ubuntu by using the 32 bit libraries.
You can use ["sudo"] and apt-get to install these libraries.
sudo apt-get install ia32-libs*
One can also use the synaptic package manager to install the 32 bit libraries.
Another option is to create a 32 bit environment with ["chroot"]. See ["32 bit chroot"]