I see plenty of good references to OS development sites, so I'll describe a different approach:
If you want the experience of implementing an OS from bare metal, there are way better hardware choices than an old PC. With the PC architecture, you will spend an inordinate amount of your time coding around uninteresting artifacts of its 30 year design history. For example, just the bootloader part of the project has probably burned out many a brave programmer.
For example, you'll need one set of drivers to read your kernel off of disk and/or the network. Then you'll need code to get into protected mode. At that point, you need another set of drivers! Very little of the work you do to get the chip into protected mode will be transferable after that point. You want to run it on a different PC +- 4 years and you'll need yet another set of drivers.
Look into bootstrapping an ARM or other 32-bit "embedded" chip. Inexpensive development boards are available, or you can solder your own! Some have built-in ethernet and usb. I think you will have more fun working on a sane, non-crusty architecture, and perhaps end up with some re-usable skills.
