Getting and installing these fonts is a somewhat involved process. First, retrieve the font(s). Next, ensure they're .pcf or .pcf.gz files. If they're .bdf files, investigate the "bdftopcf" command (ie. read the man page). Drop the .pcf or .pcf.gz files into the /usr/X11R6/lib/X11/fonts/misc dir (this is the correct directory for RedHat 5.1 through 7.1, it may be different on other distributions). cd to that directory, and run mkfontdir. Then run xset fp rehash and/or restart your X font server, whichever applies to your situation. Sometimes it's a good idea to go into the fonts.alias file in the same directory, and create shorter alias names for the fonts.
To use the new fonts, you start your Xterm program of choice with the appropriate command to your Xterm, which can be found either in the man page or by using the "--help" parameter on the command line. Popular terms would be used as follows:
xterm -font <fontname>
xterm -fn <fontname> -fb <fontname-bold> Eterm -F <fontname> rxvt -fn <fontname>
VGA fonts are available from Stumpy's ANSI Fonts page at http://home.earthlink.net/~us5zahns/enl/ansifont.html (which I have borrowed from extensively while writing this).