Hello all. I'm trying to install graphviz on a computer running Fedora 3 (Heidelberg). I downloaded the graphviz repo file from graphviz.org, and ran yum install graphviz*.

On my first attempt, I got the following messages:

Setting up Install Process
Setting up Repo: graphviz-stable
repomd.xml 100% |=========================| 951 B 00:00
Setting up Repo: base
Cannot find a valid baseurl for repo: base

I then uncommented the baseurl lines from the files in yum.repos.d, and tried again getting the following messages:

Setting up Repo: graphviz-stable
repomd.xml 100% |=========================| 951 B 00:00
Setting up Repo: base
http://download.fedora.redhat.com/pu...ta/repomd.xml: [Errno 4] IOError: HTTP Error 404: Not Found
Trying other mirror.
Cannot open/read repomd.xml file for repository: base
failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.

My file yum.repos.d/fedora.repo has the following contents:

[base]
name=Fedora Core $releasever - $basearch - Base
#baseurl=http://download.fedora.redhat.com/pub/fedora/linux/core/$releasever/$basearch/os/
mirrorlist=http://fedora.redhat.com/download/mirrors/fedora-core-$releasever
enabled=1
gpgcheck=1

I've been able to use yum on another pc, running fedora 9, but copying over the yum configuration files didn't help. What else can I try?

You can either install from source, or upgrade. FC3 is ancient, and it's not surprising it wouldn't have suport for any sort of current software. The latest version is FC11.