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/']
If you're talking about servers you **should not** be using DHCP to configure their IP addresses. This creates all sorts of headaches long-term, and even Microsoft will tell you it's not a recommended practice. 

I relate the parable of the DHCP network that got moved to CoLocation and left the DHCP server behind: Needless to say nothing worked at the CoLo and the admin in question looked looked like an idiot.

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For Desktops and Laptops by all means use DHCP, possibly in combination with static leases if you need to ensure that machines always have the same IP when they come onto your network. This is the most sensible configuration for your end users as it lets them put their laptops on other networks (home, hotel, starbucks) without jumping through a million hoops.
Maintaining a static addressed network quickly becomes a hassle with more than 10-15 machines. You can set static addresses within the DHCP server's GUI. While these are only faux static addresses they ensure that no other device can get that address by requesting it from the DHCP server and when that particular device asks for an address it will always receive the same one.