I use Xubuntu 11.10 on my 10+ years old PC (2,8GHz,512RAM, 80GB). Is it possible to upgrade to Lubuntu 12.4 when released? Am I gonna see any difference practically? Shall I have to install all my packages from the begining again?
No it is not possible to upgrade from Xubuntu 11.10 to Lubuntu 12.04.
A possible way to get around this would be to install lubuntu-desktop using Synaptic or from the command line.
Either search Synaptic for lubuntu-desktop and mark it for installation or open a terminal and run
You can then get the remove xubuntu command from http://www.psychocats.net/ubuntu/purelxde - check that you use the correct version's command here.
Be aware that any packages you have added to the default could be lost and needed to be reinstalled.
Now you will have lubuntu 11.10 - from here you should be able to upgrade to 12.04 when it is released.
Please make sure you read the release notes for 12.04 prior to upgrading.
As far as seeing any difference practically - I doubt you'd notice much, it really depends on what you use the machine for.
Before upgrading to 12.04 install
Then remove unwanted packages and upgrade your system