#3 Make it a LAN file server with FreeNAS
If you do a lot of file sharing on your network, you might have looked into using network attached storage (NAS) rather than creating basic shares with Windows. You may have also noticed that NAS enclosures (basically small computers) don't run cheap, and then you have to buy the hard drives too. However, you can create your own NAS enclosure by installing a FreeBSD-based NAS server, FreeNAS, on your old PC.
Using a NAS server means you don't have to worry about other PCs being on in order to access Windows shares. Using FreeNAS gives you a central storage place that's always accessible. It also provides better and easier control over shares. It can store user details and authenticate users. If using Windows shares, you'd have to duplicate every user account on all the computers for similar protection of shares.
Like other NAS servers, FreeNAS gives you recycle bin support. If you delete a file from a Windows share, it's gone forever. However, if you delete a file from a FreeNAS share, it will go into the trash can, where you can later permanently delete it or recover it.
FreeNAS supports many different sharing protocols: CIFS (SMB/samba) for Windows, NFS for Linux/Uniux, and AFP for Mac OS X. Plus it supports FTP, RSYNC, and iSCSI. It even has an iTunes/DAAP server, so you can share files among your iPods. It also features a built-in BitTorrent server.
#4 Run Web, Email, FTP, and other Servers with Linux
Though Web hosting prices can be very reasonable, you might find it interesting to host your own Web site. It might also be useful when developing an Intranet or when working with special applications. You could host other services, such as an email server with a POP3 and SMTP server, file access with a FTP server, or database access using a MySQL server.
The two major Web servers, the Linux-based Apache HTTP server and Microsoft's IIS (available in professional editions of Windows) server, are actually free to use.
When installing Apache, you can either install just the Web server application (and other components separately as needed) or install a Web server software distribution or package. When using Apache, it's best to install a package of servers. Apache2Triad is a great package for Windows. If using Linux, you might want to include LAMP when installing Ubuntu Server Edition.
You might want to check out a Server Room DIY series I did for a sister site, ServerWatch, on self-hosting.
#5 Turn it into a hotspot with ZoneCD
Would you like to offer wireless Internet access to your visitors or neighbors, but don't want to spend hundreds on a hotspot gateway? Well, you don't have to; you can have a Wi-Fi hotspot up and running within an hour using your old gear. One solution is ZoneCD from PublicIP.
ZoneCD is a Linux-based live CD that provides Wi-Fi authentication and Web content filtering. It boots directly from the disc and there are no changes made to the hard drive. It requires only 128MB of RAM, a bootable CD-ROM drive, and a floppy drive or USB thumb drive to store the configuration. Two Ethernet cards are also needed. One plugs into the Internet and the other into a wireless router or access point (AP).
I discuss this and other hotspot solutions in one of my books, Wi-Fi Hotspots: Setting Up Public Wireless Internet Access.
Eric Geier is an author of many computing and networking books, including Home Networking All-in-One Desk Reference For Dummies (Wiley 2008) and 100 Things You Need to Know about Microsoft Windows Vista (Que 2007).