The PPA error is because you do not need that PPA. It duplicates what is
already in the repos in Multiverse section. If you commit that source then
it will always show as a duplicated source when you use the
package manager. My advice is to remove that line or not add the PPA in the
first place.

You can now run 32-bit packages in a 64-bit Ubuntu installation. It may be
tricky with a graphics driver, though, and not worth the time spent to get
it working right You could re-install the 32-bit version of Lubuntu if your
installation is quite recent and have not invested much time in it. BTW,
the difference between Lubuntu and Ubuntu is the desktop environment, LXDE
instead of Unity. Graphics drivers work at a lower level and would work or
not in both.

For what it is worth, I have a eeePC with Atom processor and Intel graphics
chipset and 12.04 32-bit works fine. I realise that your graphics card may
be different and more of a headache, but think there is hope. Intel is
generally well supported in Linux. My eeePC has 1 GB of RAM and Unity and
KDE work fine, but think that LXDE or XFCE would be a better choice for
less RAM.