I decided that I wanted to locate the IIS data directory on a different drive. After some searching, I found a couple KB articles that helped me get it done:
KB259671 – How to Change the Default Installation Paths for FTP and the Web
KB309506 – How To Perform an Unattended Installation of IIS 6.0
These helped me put together my unattended answer file:
[Components]
BITSServerExtensionsISAPI = OFF
BITSServerExtensionsManager = OFF
iis_common = ON
iis_doc = ON
iis_ftp = OFF
fp_extensions = OFF
iis_inetmgr = ON
iis_nntp = OFF
iis_smtp = OFF
iis_www = ON
TSWebClient = OFF
[InternetServer]
PathFTPRoot=D:\Inetpub\Ftproot
PathWWWRoot=D:\Inetpub\Wwwroot
KB222444 – How to add or remove Windows Components by using Sysocmgr.exe
Then I just ran
sysocmgr /i:%windir%\inf\sysoc.inf /u:c:\install\iis.txt
per the instructions in 222444.
Worked like a champ.