Looking at the comments on reddit, I figured that I would say that luatex does resolve pdfTeX's internal limitation of 256 glyphs that I mentioned in part two, and it should directly support OpenType fonts with PostScript outlines.

However, my understanding is that the authors of luatex do not intend to make using TrueType and OpenType fonts as simple as XeTeX directly.  Instead, luatex merely makes the machinery available for someone else to build upon.  So someone will need to write a LaTeX package for luatex to put it all together, and as far as I know, no one has done this yet (let me know if I'm wrong!).  Also, while the plan is for luatex to eventually be merged back into pdfTeX, I think it is an overstatement to say that it will happen "soon".  The current luatex roadmap says that a "production" ready version will be available in August 2009.  I doubt that the merge back to pdfTeX will happen any sooner than 2010 given that.  But yes, in the long term I think luatex will be a great thing.

It also sounds like I should probably write a fourth part to my tutorial on using fontinst.  I've never personally used it myself, and when I first started working with OpenType fonts and LaTeX I wasn't aware of its existence.  Therefore, I wrote otftofd.  So it might take a bit longer to write as I will have to learn it at the same time.

XeLaTeX also has the advantage of not only giving easy access to modern fonts, but also accepting Unicode input files.

The first thing you need to do is find out if you have XeLaTeX installed, and if it is a sufficiently up to date version. This is easiest to do from the command-line:

% xelatex
This is XeTeXk, Version 3.141592-2.2-0.996 (Web2C 7.5.6)
%&-line parsing enabled.
**^C

This is the version that I am using for the tutorial, and is what comes with TeX Live 2007. I highly recommend just installing and using the entire TeX Live CD/DVD, even if you're using a Linux system that offers TeX Live packages, because, in particular for Debian/Ubuntu, I've found that the default installation often doesn't install some important packages, and it can be a pain sort through all the available packages using Synaptics or whatnot to find what it didn't install.

I am also assuming that you are using a (modern) Unix or MacOS X system. I assume that most of this material should also apply when using Windows, but if someone can comment, let me know.

Now, as an example, say you want to use the Pagella font from the TeX Gyre project. First download them and install the fonts (the otf files) as you normally would on your computer. Under MacOS X, this means using Font Book. If you double-click on an otf file it will load Font Book for you and there will be dialog with a button to install the font. If you load Font Book yourself, you can use the "Add Fonts..." menu item under the File menu to select the files. Under a modern Unix, I would recommend just placing the otf files in your ~/.fonts folder, though I think file managers like Nautilus also understand how to install fonts.

And that was all the installation work necessary; as I said, XeLaTeX is the easiest solution unless you have specialized needs. Now just create a small LaTeX document:

 
\documentclass{article}
\usepackage{fontspec}
\setromanfont{TeX Gyre Pagella}
\begin{document}
Testing XeLaTeX!
 
Greek: τεχ.
\end{document}

The fontspec package isn't necessary, but it makes dealing with fonts in XeLaTeX much easier, for example it defines the convenient \setromanfont command. You can learn more about all of its great features from its beautifully formatted manual.

The other thing you might need to know is what XeLaTeX thinks your font is called. If you're using TeX Live, like I suggest, you will have the program otfinfo at your disposal that can do that for you:

% otfinfo --family texgyrepagella-regular.otf
TeX Gyre Pagella

Note that despite its name, otfinfo will also work on ttf files, assuming that they include OpenType data in them. The other option is to use Font Book on MacOS X or fc-list from the command-line in Unix.

Now you just run xelatex:

% xelatex test.tex
This is XeTeXk, Version 3.141592-2.2-0.996 (Web2C 7.5.6)
%&-line parsing enabled.
entering extended mode
(./test.tex
...
...
Output written on test.pdf (1 page).
Transcript written on test.log.

And you have your document:

I think that is about everything you need to know, but if you try this tutorial out and find that something doesn't work, let me know.  If you have more specialized or demanding typographical needs, you may want to use pdfTeX and pdfLaTeX, and part two of the tutorial will explain how to do the necessary configuration to use TrueType and OpenType fonts with them.