Okay, here are the news. The computer is not in my hands still, because the dude lived in Madrid, however i sent one friend of mine to go there and GRAB IT ASAP. So the G4 is safe at his place by now.
For what he told me, the computer is in a perfect conservation status, not a single scratch on it's surface and booting and running software really fast without problems.
Original Leopard installation disc, original Apple keyboard and one of these button-less mac mouses. All the cables, original package mint condition and a nice 19" Sony TFT screen in working order.
About the specs, the device is INDEED an 1,5 with 64mb video Ram, upgraded to 1gb RAM and having 80gb HDD. I even got the spare 512mb ram module from the guy.
Everything went smooth as silk.
It seems i made a great buy here.
Thanks to everybody for the support.