Assuming that your OS is toasted, you could try booting from a Rescue CD such as
Main Page - SystemRescueCd and that will give you access to your system at least.
Since you're running RHEL3, you may try contacting RedHat for support. According to their website they offer maintenance support for RHEL3 through 2010. See below (source:
redhat.com | RHEL Errata Support Policy)
Red Hat Enterprise Linux (version 3):
Including Red Hat Enterprise Linux AS, Red Hat Enterprise Linux ES, Red Hat Enterprise Linux WS, and Red Hat Desktop
General Availability: Oct 23, 2003
Full Support (including hardware updates): Oct 23, 2003 -- April 30, 2006
Deployment Support: May 1, 2006 -- Jun 30, 2007
Maintenance Support: Jul 1, 2007 -- Oct 31, 2010