I've installed FC4 on one of my test pcs @ work but of course I had to set up proxy all over the place. I found a useful article in one of the fedora forums. In short here is what I did to resolve the issue:
backed up my current wget config file:
cp -pr wgetrc wgetrc.bck
& then edited it:
gedit wgetrc &
went down to the section below, change it to my proxy settings & removed comment (# sign)
# You can set the default proxies for Wget to use for http and ftp.
# They will override the value in the environment.
http_proxy = http://proxy.yoyodyne.com:18023/
ftp_proxy = http://proxy.yoyodyne.com:18023/
# If you do not want to use proxy at all, set this to off.
use_proxy = on
then edited /etc/profile and added the following 2 lines
Voila! Yum is yummy again :)