The latest version of Lubuntu can be downloaded from Softpedia
The first beta of Lubuntu 13.04 (Raring Ringtail) has also been announced by Canonical, alongside Kubuntu, and Xubuntu.Lubuntu is a distribution that aims to be a lightweight operating system, which uses the minimal desktop LXDE and a selection of light applications.
The developers of Lubuntu 13.04 (Raring Ringtail) have yet to release any important details about the new distribution, with the exception of a new Linux kernel, 3.8.
According to the developer, the 13.04 32-bit ISO requires the CPU to have Physical Address Extensions, or PAE. For the PowerPC, it is known to run on a G4 running at 867MHz with 640MB RAM.
Download Lubuntu 13.04 Beta 1 (Raring Ringtail) right now from Softpedia. Remember that this is a development release and it should NOT be installed on production machines. It is intended to be used for testing purposes only.