What command do I use to run the auto installer for plesk reloaded on redhat enterprise 3?

I already downloaded it to the server just need to know how to execute it?

The answer to your question is in the release notes for the autoinstaller (I grabbed these from the rhel3 autoinstaller):

Plesk Install Procedure
========================

1. Log in as "root" and change your working directory to the directory where
the Plesk Autoinstaller resides; for example: # cd /home/admin/plesk

2. Set execute permission for Autoinstaller:
# chmod +x psa_installer_v2.0.0_build72040920.10_os_RedHat_el3_i686

3. Run the Autoinstaller:
# ./psa_installer_v2.0.0_build72040920.10_os_RedHat_el3_i686

4. Follow on-screen instructions.