After the "prepare for image capture" does it actually reboot to PXE and then fail? You should watch the system you're capturing and see if it attempts to come up to PXE or not. If it actually reboots back into production, the capture image task will fail, very quickly, because GHOST is not intended to run in production.
Be sure the BIOS is set on the system to boot to the network as a first option, or it wont even try. OR you can install Automation Folders on the system, and then we can boot to automation that way. No matter what you do though, it will NOT successfully capture an image unless you can boot into an automation environment (generally done by using PXE, but not always). The automation environment allows us to isolate the production environment (no files in use) and capture a clean image. If you're actually IN the OS, then we get a bunch of ... well, it's not good, so we have to get into WinPE somehow. (Or Linux if you prefer.)
So, per the previous comment, if you use F12 to manually choose to boot to PXE, or something "like" that it will help.
There are some additional caveats though if you do. 1) PXE services are not, by default, enabled in DS 7.1. If they're not enabled, then even if the client system attempts to find a PXE server, it will not get a response and boot into production. These are started manually (unless you change the service settings) in Service manager. 2) you have to have a configured/built Preboot envirionment. To do this, you need to got o Settings | Deployment | Preboot whatever, and make a new PXE environment. 32 bit is generally OK. Remember, this is for PXE, and there is a different process if you choose to use Automation Folders instead. Once you make this, you then have to 3) allow BootWiz to run on the server and/or site server(s) to make said environment and ready the PXE services. This takes time, and patience is required.
That's the short version. If you've not done the above paragraph, or are unfamiliar with it, then my guess is you can not, yet, PXE boot, even if you've configured the system to do so.
We have some getting started guides and such that can help you through these processes. Detailing it all here is... fascinating.
There's also a quick trick you can try just to see if you CAN PXE boot. Create a task to "Reboot To" and set it to PXE. If you can make this task, test the system to see if it will do it. If it does, and you end up in WinPE, you're set to run your job again. If you can not, then you're not ready. When you build the task, you'll be prompted to select a PXE image, if there is none, then you haven't done step 2 in the above paragraph. If you CAN select it, but when you get to automation, there is no image, then step 3 may not have run, and possibly step 1.
OK - all of that is how to make sure the background actions have been taken to prepare your system for this process, IF you're using PXE. Unfortunately, there is no good shortcut for getting PXE servers up and running, no matter what product you're using.
Let us know what you learn! Again, there are some pretty decent getting started guides and such out here. :D