Or get libxml2 from
http://www.libxml.org/
[download]

Query your OS package management, or check manually to see if this is installed. If this isn't installed, do so:

If you install via RPMs, make sure you also install the -devel
RPMs, as this is where the headers (.h files) are.
[download]

The site indicated provides the downloads requred should you not be able to use your OS package management tool. If none of this makes sense read the module documentation (including the README) or speak to your systems administrator.

Please don't ignore formatting advice displayed when posting. See How do I post a question effectively?.