If you wanna test the new Plone alpha release (Plone4.0alpha1) you’d need a 2.6 installation. If you are using your VPS and 8.04 LTS as your rock OS, you won’t want to upgrade just for the python version. More here

Instead of building it yourself, the non debian way, you should use a package. That’s very easy with Launchpad’s rocking PPA feature.