The thing about Android is that to run it in a laptop it has to be run in a virtual machine. from what I understand this is how it is run in phones as well, but the VM is the entire interface.
At this point in time though, Android is not really set up to run as the principal OS in a standard rig.
That I know of, the closes thing to that is the netbook made for the motorola xoom, and that runs a modified version of ubuntu Linux (don't know which version), with the android side being in a VM.
You are better off just taking your old rig and running a Linux distro of your preference on it. It will give that machine an entire new lease on life.