When you say you have added driver files, you have not mentioned what version of Ghost you have added them to, but if it's 11.5.1.2266, then have you added Vista 32 bit drivers as that is what WinPE expects.
I suspect you may have problems finding Vista drivers for a server, but you may find suitable drivers for the chipset being used for the disk subsystem by checking the chipset vendor's website. Alternatively, you may wish to try building the WinPE 3.1 workaround detailed in this article:
https://www-secure.symantec.com/connect/articles/creating-and-using-winpe31-image-gss-251