Adding new hardware to existing system

[David.Grudek@anixter.com]

I am new to debian and looking for some help.  I have been practicing with 
debian installs also adding new hardware to existing systems.  I tried 
adding a new nic and a harddrive to a system.  I could not get either to 
work.  When I take the beta 4 sarge install disk and run the install it 
detects both pieces and they work, but if the unit was built with the same 
cd and then add the hardware it does not work.  What steps should be taken 
to add a new piece of hardware like a nic card and or hard drive for it to 
be detected.  I used a fedora system and it detected it just fine.  When i 
installed the hard drive I did a fdisk /dev/hdc and it did not work said 
no device  Any help would be appreciated.