Apache is case sensitive on *nix systems, since the underlying file system is case sensitive. This can cause trouble with sites brought over from case-insensitive systems. It is relatively easy to remove that sensitivity with the apache module check_speling (funny name, huh?). It will also remap mistyped urls when possible, mapping index.htm to the proper index.html, etc.

This is the procedure for Ubuntu/Debian systems.
From the command line, type sudo su to get root privileges.
nano /etc/apache2/mods-available/speling.conf
Type CheckSpelling on and hit ctrl-x, y to exit and save the file.
type a2enmod and then speling and hit enter.
type /etc/init.d/apache2 reload to reload apache.
Mistype a url to test it.