I haven't used FIRM since switching our environment to Windows 7. For some reason FIRM Prod thinks that our "System Reserved" volume is the production volume, and the drivers get copied to a location that is not available during Sysprep/OOBE. I have no idea how it decides what is production or not, but it does appear to be a bit of a fail with out W7 images. Xcopy is the answer, and we need to specify "D:" as the target location.
To be honest, I now run a batch script that checks all drive letters for a "%:\BootMGR" and sets that as "%___Drive_SR%" and then again for "%:\Windows\System32\explorer.exe" and sets that to "%___Drive_OS%". I then use these values to set the BCD and perform any required file copy operations etc. Works a treat. I like having more control than less - as is the case with Firm and the fact that nobody seems to know how exactly it works.