Some parts of this site employ Unicode characters. Unicode is a standard for representation of language scripts, that supercedes the old ASCII and ANSI still in use.
ASCII encodes 128 characters that include the English alphabet, the digits, the line break, the tab and the space, as well as many punctuation symbols and others. ANSI comes in several flavours, but in short, it allows encoding of up to 256 characters (of which the first 128 are the ASCII ones). This is not enough to encode all the special characters found in the many languages that employ variants of the Latin alphabet; it does not include other alphabets; and it is not nearly enough to encode Chinese ideograms, for example.
Unicode is a standard that assigns a number and a name to each character in each of the languages and scripts it supports (as well as math symbols, drawing symbols, dingbats, and the like). There are very few fonts that include all these characters. Most Unicode fonts include the basic letters of the Latin alphabet with special diacritics like accutes, graves, breves, macrons, ogoneks, dots above and below, etc. The Greek and Cyrillic alphabets are usually included too. Larger fonts are needed to encode the tens of thousands of characters used in Japanese and the Chinese languages, as well as Korean. Other fonts support symbols of the IPA (the International Phonetic Alphabet), and so on.
Some time ago Microsoft released a free font pack with fonts like Arial, Times New Roman, Georgia, Impact, Trebuchet MS, etc. that include an important chunk of Unicode. These are still free, and I think some larger versions come with Windows XP and Microsoft applications for XP. You can download them at http://sourceforge.net/project/showfiles.php?group_id=34153&release_id=105. Other Unicode fonts you can search for in the Internet are Gentium, Code2000, SilDoulosUnicodeIPA, and Lucida Sans Unicode. In Google: http://directory.google.com/Top/Computers/Software/Fonts/Multiscript_Fonts/.
If you can view the following characters correctly, then you already have a Unicode font installed in your computer:
ā
ē
ī
ō
ū
(that’s a e i o u with macrons, i. e. horizontal lines on top)
ĕ
ŏ
(that’s e o with breves, i. e. U-like curves on top)
Ā
Ē
Ī
Ō
Ū
Ĕ
Ŏ
(same as above, in uppercase)
If any of the above appears to be incorrect (for example, if an empty square or an ordinary character other than described appears in place of the Unicode character), then you need to download and install a Unicode font that supports at least up to the Latin Extended-A subset of Unicode.