This is quickly done and I would have like to modified the gui a bit but it uses glade which I can't do nothing with (well, I can't do much with much else but you get the point...)

If you value battery life, you probably don't want this. It wakes up the screen and uses a lot of cpu.

If you want to install it, get the *.deb files from http://qwerty12.maemobox.org/xscreensaver/ and use dpkg -i.

Namely:
xscreensaver_5.07-1_armel.deb
xscreensaver-data_5.07-1_armel.deb
xscreensaver-data-extra_5.07-1_armel.deb

If you want to be able to see the settings window properly, install:
wmctrl_1.07-6_armel.deb

You may need to install libxxf86vm1_1.0.2-1_armel.deb as xscreensaver depends on it.

Post 6 contains a daemon that will automatically start and stop xscreensaver if your charger is plugged in and not plugged in respectively.