by the sound of it you are new to Linux
It means you need to install rtld(GNU_HASH) before you install hylafax try yum install rtld
you could also try yum localinstall hylafax-4.3.4-1rhel5.i386.rpm that may resolve the problem as well
if they both don't work you will need to get the file else were make sure you get the right version number it told you to install
Sorry you are wrong here. The OP is using SME Server 7.3 and hence is installing the wrong version of the application as SME Server 7.3 is based on Centos 4.6, which is based on RHEL 4 (el4) and not RHEL5 (el5), which OP is installing.
OP should try and get hold of a el4 version and even better look for one in the default configured repositories or the SME Contribs repository, or if that all fails might consider Dag or atRPMS, but for newbies that might turn out to be a bit out of their league.
I suggest OP to look at this page in the wiki:
http://wiki.contribs.org/HylaFax