An android tablet is already running linux. It is what the operating
system is built on. The graphical interface is just built using something
similar to java, rather than the usual Xorg. There are not currently any
Android tablets that can plug and play with the default linux OSes that are
popular like ubuntu that I am aware of. The drivers are not present in
the kernel. There are sites like xda-developers . com that regularly
modify Ubuntu and debian to work on a specific tablet. But then you are
without security updates, etc.

There are some options that give a sort of dual boot, using chroot, to run
debian (there is an installer in the market) but it is sort of complicated
and buggy still...