Turn your old PC into NAS (Network attached storage) server with FreeNAS.
FTA "...FreeNAS, an open source NAS server, can convert a PC into a network-attached storage server. The software, which is based on FreeBSD, Samba, and PHP, includes an operating system that supports various software RAID models and a Web user interface. The server supports access from Windows machines, Apple Macs, FTP, SSH, and Network File System (NFS), and it takes up less than 16MB of disk space on a hard drive or removable media.
FreeNAS is free to use and deploy without cost. It's an open source project published under the BSD license. The software is popular enough to have gotten more than 20,000 downloads last month..."