Red Hat Enterprise Linux support periods (again)
Sometime I will merge this information into RHELSupportPeriods, but for now, see here. RHEL 5 has security updates through March 31s 2014.
The UofT's Red Hat Network access
The UofT has a site license for Red Hat Enterprise Linux. However, you don't deal directly with Red Hat; instead you have to go through our local people and the local RHN proxy, which is found here.
(Hopefully this will save me having to re-find this information every time I need it.)
Stuff and notes about the ASUS M2N4-SLI motherboard
See also AMD64Stability.
Red Hat Enterprise Linux support periods
It is surprisingly hard to find this information on Red Hat's website; you'd think the support periods for the various Enterprise Linux would be somewhere on the product pages for each EL release, but they're actually hiding off in the Security Updates section.
The short answer is that security updates are done for seven years after the initial release. RHEL 4 was released Febuary 15th 2005, so security updates will be available through the end of February 2012.
This means that CentOS will also have updates for that long, since they build from Red Hat EL's source RPMs. Even if the CentOS project goes away as an organized entity, a CentOS install can just grab the RHEL update source RPMs and rebuild them directly.