Is it possible to install a new operating system like ubuntu on the Surface, instead of windows 8?
At the moment, there are no known ways to install any OS other than Windows RT on the Surface tablet.
Windows 8 has a feature called Secure Boot. It basically prevents the installation of operating systems that do not have prior approval from Microsoft.
Surface is an ARM device and it runs Windows RT and has Secure Boot built in. At the moment, there are no known ways to disable Secure Boot. So the first step to installing other Operating System on Surface would be to disable Secure Boot.
I think its only a matter of time before some clever hacker comes up with a solution. Lets wait patiently.
I think for now, the simple answer is no. This may change over time, the surface is new, people haven't figured out ways of hacking it just yet. I believe the bootloader on the surface is very locked down using that SecureBoot feature.
IF Oracle (or friends) decide to develop an ARM-based VirtualBox, then you could at least run Ubuntu in a virtual machine on the Surface.
I have also read that currently it is not possible to use any of Microsoft's Hyper-V stuff on the Surface, but once again, this may change over time.