how upgrade works?

[Ritesh Bharati]

hi,
I was trieng to upgrade of 7.3 to FC1 using apt , Which  failed , then 
was wondering how FC1 upgrade process work. 
I have rh7.3 installed and I tried to upgrade it to FC1 using apt-get 
-f  -y -d -o dist-upgrade  Dir::Cache::Archives=/temp/upgrade . BUT it 
failed with pre-depends . I tried to  Hold those packahes in apt 
upgrade, no use.
I tried to apt-get install on all installed packages on m y RH7.3... 
again i got pre-dependency list.. :)... dependency cycle....
There are may rpms in  RH7.3  whcih are replaced by other rpms in FC1. 
Can somebody throw some light on ... How pre-dendency / dependency cycle 
is taken care by FC1 upgrade process. How upgrade works ??
This could lead to hope of light to other developes who want to upgrade 
their boxes using apt-get/yum ..

thanks in advance
Ritesh Bharati