The following are several important paths that you may need to know when writing and configuring scripts.

ImageMagick = /usr/local/bin/convert
MPlayer = /usr/local/bin/mplayer
Perl = /usr/bin/perl
PHP = /usr/local/bin/php
Sendmail = /usr/local/sbin/sendmail
Curl = /usr/bin/curl or /usr/local/bin/curl

Your home root: /home/username/
Your 'www' directory: /home/username/public_html/
Your cgi-bin: /home/username/public_html/cgi-bin

Note: Depending on which script you're installing, you may need to use these paths either with or without the trailing slash ("/").