Question : Changing Windows 2003 Network Subnet

So, I got a nice VPN solution with my new firewall but am having many issues setting up the VPN because I use the defacto 192.168.1.x address scheme.  I want to change that to 192.168.12.x.  Everything is staying exactly where it is and I just want to change the addresses.  

Can you please assist and tell me what to expect or if what I am planning has any flaws.  
1. I will change the IP on all my web gui devices first.  Since after I change over I won't be able to access them.  
2. I will then make the change on the firewall/gateway.  Changing all address objects to the new 12.x.  
3. I will then tackle the switches.  Changing the VLANs on all the switches.
4.  Finally what actually scares me, is changing the DC's.   Change the IP and DNS, followed by Ipconfig /registerdns and dcdiag /fix on both.  
5. Delete all DHCP leases and change the scope.
6. now do all servers.  Exchange, FIle, BES and so forth.  Doing an ipconfig /flush and register as I go along.  

Everything else is DHCP.  

Am I missing anything.  Should I do anything differently.

Answer : Changing Windows 2003 Network Subnet

2003 or 2003 R2?  Not that it would make any difference.  

If the additional space needs to be added to the C:\ drive then you will need to do it from a boot disk.  If it's any other drive than the OS drive, you don't need to do it from a boot disk.

You will need to select the disk, then the partition before running the extend command.