http://www.senet.com.au/~cpeacock/serial1.htm: very detailed information about interfacing the PC with good examples by Craig Peacock.
http://www.colargol.idb.hist.no/~bardj/serial/: The Serial Port, C. Blum, B. Johannessen, et al. The site also contains useful information about the serial port with examples.
http://www.linuxdoc.org/HOWTO/Kernel-HOWTO.html: The Linux Kernel HOWTO, by Brian Ward, bri@blah.math.tu-graz.ac.at about compiling a new kernel.
http://www.linuxdoc.org/HOWTO/Serial-HOWTO.html: The Linux Serial HOWTO, revised by David S. Lawyer, bf347@lafn.org, original by Greg Hankins, contains some serial port hardware information.
http://www.linuxdoc.org/HOWTO/Serial-Programming-HOWTO.html: The Linux Serial Programming HOWTO, by Peter H. Baumann, Peter.Baumann@dlr.de, contains an example of using the serial port device driver.
All listings referred to in this article are available by anonymous download in the file ftp://ftp.ssc.com/pub/lj/listings/issue68/3326.tgz.