Chromium was not in the official repositories during 8.04. 8.10 was the first. Next to that Google Chrome 12.0.742.60 beta is not Chromium. Google chrome is the actual version Google released. But even Chrome was released for 8.10+ only.
You could check synaptic for the package. Maybe it gives a hint to where you got it from.
But most likely you installed it from source.
You can find a september 2008 release of chromium here: http://media.codeweavers.com/pub/crossover/chromium/ But this is based of of Lucid, not Hardy.
Other option would be to try and install Google Chrome from their website It is more than likely to complain if your system is too old for it but it would not surprise me if you got this up and running even on 8.04. Chromium from the latest release might be a stretch.