Here are the steps followed to build one 1.4 on CentOS 5.5

This doc is to complete/correct 

http://www.opennebula.org/documentation:rel1.4:notes

1. do not install rpm with yum localinstall if you do not want
signature problems
- wget ...
- rpm -ivh ...

2. Needed packages for all the following :

wget http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm

rpm -ivh epel-release-5-3.noarch.rpm

wget http://prdownloads.sourceforge.net/scons/scons-1.2.0-1.noarch.rpm

rpm -ivh scons-1.2.0-1.noarch.rpm

yum install gcc
yum install gcc-c++
yum install libxml2-devel
yum install libxslt-devel
yum install expat-devel
yum install curl-devel

3. Gems fun

gem install nokogiri rake

(xmlparser needs rake)

and 

gem install xmlparser

4. Time to xmlrpc

The rpm provided in the documentation doesn't work anymore.

get the 1.06.40 source :

wget http://sourceforge.net/projects/xmlrpc-c/files/Xmlrpc-c%20Super%20Stable/1.06.40/xmlrpc-c-1.06.40.tgz/download

and install it with

./configure
make CADD=-fPIC (my system is 64 bits, see doc/INSTALL for more information)
make install

libs under /usr/local/lib, so if not present in the conf do :

echo "/usr/local/lib" > /etc/ld.so.conf.d/one.conf
ldconfig

5. scons peacefully ;)