If you have never worked with SGML, look at the SGML home page (http://www.oasis-open.org/cover.html), or read Gentle introduction in SGML (http://www-tei.uic.edu/orgs/tei/sgml/teip3sg/index.html, A Russian translation is available from http://xtalk.msk.su/SGML).
You don't have to type in all those tags manually. There are many SGML editors out there already. I use psgml, which is a powerful SGML mode for Emacs, handy and free.
TEItools was inspired by the idea of SGMLtools (previously known as SGML-tools, previously known as linuxdoc-sgml, and mirrored right here). But the straight forward replacement model SGMLtools uses does not give enough power to produce really good documents, and its RTF output is unfortunately unusable. So, because one of my motivation was to be able to write MS Word documents in the comfortable Emacs environment, I had to create my own tools. But I owe a lot of thanks to the SGMLtools team.
TEItools is a coupled set of scripts, written in Tcl, which does various SGML transformations. Currently they include the following converters:
Not all of them are of equal quality. My own main working horse is TEI Lite DTD, so TEI Lite to something converters are arguably the most sophisticated. On the other hand, refining existing and implementing new converters is not too formidable. It's just time consuming and I do not work on these full time.
Besides the above mentioned "mainstream" DTDs, a set of home grown DTDs is supported, including the following converters:
Also included is a set of CGI scripts, including those for showing TEI and Open eBook thought the Web.
Others may have been added at the time you're reading this.
After installation, using TEItools is as simple as running
$ tei2tex MyGreatDocument.sgml
Last modified: þÔ× æÅ× 19 18:09:48 MSK 2004
Produced by TEItools