We have an environment where we have blasted a prepped Windows image out to multiple machines. We now need to customize the networking settings on each image en masse.

What tools exist to modify that image and customize the IP address/netmask/gateway post-imaging?

I would also look at a commercial solution that is able to deploy and customize Windows images as long as it runs on Linux and is fully scriptable.

To clarify, my order of operations is:

* Server PXE boots
* Various Things are done to the hardware to prep it
* Image is copied onto the hard drive
* Image is customized (network settings)

(Naturally, if such a deployment tool exists that can do the last two in one step, I'll take that)
['https://serverfault.com/questions/107330', 'https://serverfault.com', 'https://serverfault.com/users/2101/']
DHCP is the only choice (IMHO) when you get over 5 or 6 machines ( and even then ... ) 

In your case I would also setup dDNS so that your hosts register in DNS when they get a DHCP lease, so if you know the host name you know the ip address. 

As far as host needed a static IP address. The best way is to let them configure off DHCP, but in the DHCP configuration reserve the IP address for that machine's MAC address. This lets you not have to manually configure IPs but still have "static" ip addressing.
Here's your main issue (as stated):

> 
> **"We don't have access to the DHCP server"** 
> 
> 
> 

Why don't you have access to your internal DHCP server? **(fix this!)**... Your number of clients concords with most environments using DHCP (recommended). Yes, static IPs would drive you nuts!