Download and untar source files

lame is not available through a yum repository; but it can be obtained and installed from Dag Wieers' RPM repositoryrpm -ivh http://apt.sw.be/redhat/el5/en/i386/RPMS.dag/lame-3.97-1.el5.rf.i386.rpm

You may wish to check that the link specified here is actually the latest and greatest. Look at the files available on Source Forge and pick the latest one there. 
cd /usr/src 
Get the latest released version of zaptel
wget http://downloads.digium.com/pub/telephony/zaptel/zaptel-1.4.x.tar.gz
tar zxvf zaptel-1.4.x.tar.gz 

Get the latest released version of Asteriskwget http://downloads.digium.com/pub/telephony/asterisk/asterisk-1.4.x.tar.gz
tar zxvf asterisk-1.4.x.tar.gz

wget http://downloads.digium.com/pub/telephony/asterisk/asterisk-addons-1.4.x.tar.gz
tar zxvf asterisk-addons-1.4.x.tar.gz