Do you want something to tinker with, or do you like the "set-it-and-forget-it" option?
I'm a fan of Windows Home Server for home --it's reasonably simple, and its backups are excellent. One advantage of WHS is that not only can it bare-metal backup your systems, but its backup is smart enough to not backup duplicate files --for example, if three of your systems have identical iexplore.exe files, it will only keep one copy of the file, saving you space. All you have to do is install the Windows Home Server client on a workstation to connect it to the server, and it will begin backing it up automatically --it's that easy.
You could either build a server yourself and buy an OEM copy of Windows Home Server, or you could get a pre-fabbed model from HP, Lenovo, Acer, or others. Of the pre-fabbed models, I'm partial to HP's MediaSmart EX490 (I own one, and it has one of the better hardware configurations IMO).
If you want to build one yourself, it doesn't take a lot. A simple low-energy dual-core processor like a Celeron 3xxx, or a Pentium dual-core E5xxx are ideal. 2GB of RAM runs Windows Home Server quite well, and you can buy a micro-ATX board to run it all, with onboard video. Just make sure you have enough SATA ports for drive expansion, and you're good. Windows Home Server will make multiple drives look like a single large one, and if you have more than one drive, you can turn on Folder Duplication which will keep duplicate copies of your files to guard against a hard drive failing and taking your data with it.