YUM Problems after Initital FC5 Install

[Chalonec Roger]

I have installed FC5 but when I run YUM is get lots of different errors
so I ran yum clean all.  Most errors went away but now I have:

Header not complete

I tried yum clean all again but that did not do anything.  I am behind a
transparent proxy server. Are there any known problems with proxy
servers?  Does FC5 YUM use any special ports?  Does anyone know what
port YUM uses to communicative?  Is it a TCP port?

Thanks,

Roger