When trying to figure out driver support for WinPE I stumbled on two articles on how to add drivers in the automation environment. There is an article on how to do this on kb.altiris.com, but I was never able to get it to work properly. After some messing around I found an easier way to do this.
After you click finish the second wizard will walk you through the rest of the build.
The last thing to check is to make sure your you initial deploy is set correctly.
After running through all these steps I found this easier to modify and configure the WinPE 2.1 for Deployment Solution 7.0 than to use the script and manually copying your files into the WinPE file structure.
I hope this also works for you.