Case 1. If your system installed in the controller volume, you will needed a installation driver disk.
in this case, you can use the Centos 4.4 installation disk.

  ftp://ftp.areca.com.tw/RaidCards/AP_Drivers/Linux/DRIVER/CentOS/CentOS-4.4/

Case 2. if your system installed in a seperate drive, and you want to install the controller driver module only
you can download the RPM module for x86_64 from following link :

   the x86_64 RPM here 
   http://downloads.scalableinformatics.com/downloads/Scientific_Linux/4.4/x86_64/RPMS/arcmsr-1.20.0X.13-1.x86_64.rpm 

   the x86_64 SRPM here 
   http://downloads.scalableinformatics.com/downloads/Scientific_Linux/4.4/x86_64/SRPMS/arcmsr-1.20.0X.13-1.src.rpm 


Many thanks for the support by Scalable Informatics LLC.