Try out a Via C7-based machine (Score 1)

I have one of these in my kitchen (long story) that has been happily chugging away without any downtime for about a year now.

These processors/computers are certainly now the highest-performance machines in the world, but they handle most home tasks wonderfully and consume almost no power when idle. For 24/7 operation this becomes very important. Also, most varieties of C7 can operate with passive cooling, meaning your power supply fan will be the only noise it generates.

If you can afford it (I put mine together with a gig of memory, 500gb disk, and DVD for about $350 a year ago), this is a better approach than "throw slackware on an old Pentium 3" because you can get the same or better performance without the ongoing electricity cost and loud operation.