Installing from CD

All,

I'm trying to launch a series of INF files from CD. They're only half-working, and I'm at the limit of my experience to get them working all the way. Here's a snippit from one such INF:

[VERSION]
AdvancedINF=2.5, %AdvPackWarn%
signature=$CHICAGO$

[DefaultInstall]
RunPostSetupCommands	= Do.Install
AddReg			= Set.Next

[Do.Install]
%01%\WU\904706.EXE /q:u /r:n
;...
"runonce -q"

[Set.Next]
HKLM,"%KEY_RUNONCEEX%\",Title,0,"Getting to the good stuff..."

HKLM,"%KEY_RUNONCEEX%\100",,,"7-Zip 4.32"
HKLM,"%KEY_RUNONCEEX%\100",1,,"%01%\PKG\7z432.exe /S"

[Strings]
KEY_RUNONCEEX="SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnceEx"

;Localizable strings
AdvPackWarn="You need a newer version of advpack.dll."

Ok, %01% is the DIRID for the full path to where the INF is installed from. In this case, it's D:\SOFTWARE\

In the first instance, in the [Do.Install] section, the DIRID is not getting expanded correctly.

In the second instance, where it's creating a RunOnceEx entry, it works fine.

Anyone have any tips or suggestions on how I can identify the CDROM drive letter?

TIA,