Use the edit /etc/wfe/conf/settings method mentioned in the posts that I linked above. You'll need to boot from some other live linux distro to get access.
If the config currently on the system is not important, the easiest thing to do would be a fresh reinstall from ISO.
Seven years ago is like yesterday. ;P Considering that one of the AV engines has changed, it's doubtful that a v5 install could even get some current pattern updates.
As Scott mentioned, boot from a live/rescue CD and change the web password in the file he mentioned. After that, you should be able to change the root password from webadmin.
I personally use RIP Linux as my preferred rescue CD.