CentOS on home machine HD

[Roger]

I've not experimented with server systems for many many  years so would 
like to understand a few points.

On my home machine I have 2 hard drives one has 2 partitions, Ubuntu on 
the first and Fedora which I use most on the second partition.
the pc boots through the Ubuntu grub.

I have Fedora 16 on the second drive but don't use it.
If I install CentOS on that Fedora hard drive with the first drive 
unplugged it should be a fresh install.
Questions:
When I switch on the first hard drive and cold boot, I can choose on 
bios boot between the centos and nix drives, Centos should not know of 
the other's existence is this correct.
As a server, the Centos drive would permit access to 3 ip addresses.
It will have LAMP stack, latest Ruby and Rails and Drupal 7 for development.
Is it possible, while the pc is switched on during the day to use the 
CentOS as a server for development without affecting or accessing my 
working Linux installations?
Will a thompson gateway TG782T ADSL modem/router be sufficient to act as 
a basic server modem for the above proposal.
I hope I've explained it well enough.

I'm thinking about getting something like a HP6200 for a server but want 
to learn first before parting with cash.