Very easily doable.
For straight DVR stuff, any PC will do. Great details are available over at another site, the green button dot tv.
The best, easiest whole house DVR solution is Windows Media Center. (Use Windows 7 for the best results.) All setup and recording and guide management and whatnot is done on one PC; remote TVs are handled via WMC extenders, usually XBox (could also be Ceton Echo). The extenders are special instances of remote desktop into that single PC, so all "set, watch, delete recordings" can be done from anywhere and it all actually happens on the main box.
I've taken off the shelf PCs, added tuners and a hard drive, and made them into WMC machines.
Some people hook the PC straight to the TV; you'll need a PC or a video card that has suitable output, such as HDMI; you'll also need a WMC remote control setup, with IR receiver and a suitable remote.
Other people sit the PC somewhere remote, and simply use an extender at each TV. There are pros and cons to each approach.
The key for stability is, set the machine up to be a DVR and pretty much nothing else.