[CentOS] Nessus Installation Failure

I'm trying to get get nessus 2.2.5 to install on my centos 3.5 system.  
It errors out with this error:

Press ENTER to continue

x - Compiling the libraries
x -- Configuring the sources for your system
configure: error: Could not find OpenSSL and OpenSSL headers on your system
**** An error occured :/
Do you want to save the compilation log to analyze what went wrong ? [y]
Where should I save this file ? [/root/nessus_compilation]
Do you want to delete /tmp/nessus-installer.11739 ? [y]


rpm -qv openssl shows:

[root at asskicker em]# rpm -qv openssl
openssl-0.9.7a-33.15

Anyone have any ideas as to what I'm doing wrong or what I need to 
change to get this package to install? 

Thank you,

Ed