Changing the default X11 Cursor

Very trivial.
Unpack your cursor package to ~/.icons/.
The directory structure should be:
~/.icons
~/.icons/theme_name
~/.icons/theme_name/cursors

Create a symbolic link between ~/.icons/default and the theme_name and restart X.
ln -s ~/.icons/theme_name ~/.icons/default

If you have any issues, remove the symbolic link:
rm ~/.icons/default
create a ~/.icons/default directory
mkdir ~/.icons/default
and insert the following file (index.theme) into the ~/.icons/default directory:
touch ~/.icons/default/index.theme
vi ~/.icons/default/index.theme
1 [Icon Theme]
[...]

Changing The Default X Cursor

Although it took me ages to find out how to change the default X cursor the solution is simple.
1. Install the icon/cursor theme using your default package manager (or extract it to /usr/share/icons)
2. List the contents of your /usr/share/icons directory

~ %  ls /usr/share/icons [truncated output]

Chameleon-Anthracite-Large/    Chameleon-Anthracite-Small/ 
HighContrastLargePrint/         LowContrastLargePrint/  gnome/

3. Copy the name of the cursor theme [...]