I am facing the same problem since past few months. Just a recap:
1) System is Zotac Zbox ID18 (barebones)
2) SSD connected in AHCI mode, 2GB RAM installed
3) Using Sandisk Cruzer Blade and Kingston DT SE9
4) Use DriversPack 10.6 to slipstream
5) Use RVM Integrator 1.6 to generate ISO
6) Use Rufus 2.10.973 to write bootable ISO to Sandisk/Kingston
7) I have to force my USB to HDD Mode to boot up on ID18
8) The 1st stage of installation goes fine, i.e. contents get copied from USB to SSD
9) After the first reboot, in the 2nd stage, I get the following errors:
"Windows cannot find '\OEM\bin\un7zip.exe'..." and "C:\DSPdpblr.exe"
It is interesting to note the drive letter is missing in first error. I backtracted the errors to I386\presetup.cmd:
SET TAGFILE=\OEM
FOR %%i IN (C D E F G H I J K L M N O P Q R S T U V W X Y) DO IF EXIST "%%i:%TAGFILE%" SET CDDRIVE=%%i:& GOTO DPsFound
Start /wait /realtime /separate "" %CDDRIVE%\OEM\bin\un7zip.exe %CDDRIVE%\OEM\DP*.7z %SystemDrive%\
I confirmed by adding additional code to this file and booting again, that CDDRIVE was never found, hence it was blank. The question then is, why was it not found. The only reason I can see is, after the 1st reboot, in the 2nd stage, when the WinXP came up, the USB flash drive was not mounted. Hence the unzip commands never got executed, and the new drivers were never installed, esp. Chipset drivers. If I just ignore this error, the 2nd stage of the installation goes fine. But after this, when the 2nd reboot happens and the OS comes up for the third time, I get blue-screen error, which I think is because the non-Mass Storage drivers never got installed. I am not able to get past this error, and I am stuck on WinXP installation on modern computer.
Please feel free to correct me. I will try to use some old USB stick which will hopefully work with XP without addl. drivers.