I ran across this bit about building a RAID that I thought was very intresting. Its not all that uncommon now adays though. In the recent past I built myself a 400$ machine that was supposed to be the house server (turned out latter the RAM was bad, killed the machine a good bit, etc etc). There is alot of good stuff you can do, with just a tiny bit of work.
The machine originally started out with 3 NIC’s (partly for fun, partly because it was a data server). It did PPPoE for the DSL, Passive proxy (Using Squid), SNMP monitoring, and a number of other things. The nice part is once you have the machine up and running (it had 2x80gig SATA drives in a RAID 1) you could add a 3ware Card and a number of cheap SATA drives in a RAID 5 for very cheap. Now the house server turns from a central DSL server, into the file storage server. If you move alot of data around on your home network, I really recomend a gigabit switch (and gigabit nic’s to match). Suddenly your transfers go from 80megabits/s to 250megabits/s (or more, if your cards/computers are decent).