I just recently set up my fileserver at home. I'd never so much as touched a Linux box before in my life, but my sister had this old PIII 800MHz 128MB H.P. Pavilion lying around collecting dust, so I installed Xubuntu on it. I got Samba up and running so I could access my share from my Windows machines, then I installed a LAMP stack and Torrentflux. Now it's a fileserver and a torrent client.
Unfortunately I still need to acquire some real storage space for it (only running on a 20 or 25 GB HDD right now). I need to find a SATA PCI card that will work under Xubuntu, and then I plan to get a couple of 500-750GB drives to stick in there.