Well I've had no luck finding a variable anywhere which sets the default temp folder for the machine (as opposed to local users). What I ended up doing though was writing a script to export the registry at cmdlines.txt and GuiRunOnce to compare the changes... thought this may come in handy for other things. The common setting of TEMP=C:\Windows\Temp or such was already set by the cmdlines execution stage so I'll set the variables then (assuming they're not overwritten again!). What I also noticed in the setuplog.txt after installation was that the cmdlines execution is just moments after Virtual Memory is set: 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\syssetup.c,3939,BEGIN_SECTION,Setting up virtual memory 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,SetUpVirtualMemory: ENTER 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: C:\, spc=8, bps=512, freeclus=723262, totalclus=1024372 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: C:\, FreeSpace = 02962481152 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: C:\ had 120586240 byte pagefile, new FreeSpace = 03083067392 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: Free space on C:\ is 2940 MB 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: D:\, spc=2, bps=512, freeclus=1006242, totalclus=1020568 02/12/2008 12:49:28.427,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: D:\, FreeSpace = 01030391808 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: Free space on D:\ is 982 MB 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: E:\, spc=8, bps=512, freeclus=635675, totalclus=640702 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: E:\, FreeSpace = 02603724800 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,BuildVolumeFreeSpaceList: Free space on E:\ is 2483 MB 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,SetUpVirtualMemory: loc 1 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,Setup configured the system to place a 768 MB pagefile on drive C:. 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,Crashdump was enabled. 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\log.c,133,,SetUpVirtualMemory: EXIT (1) 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\syssetup.c,3947,END_SECTION,Setting up virtual memory 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\syssetup.c,3958,BEGIN_SECTION,Processing [RunPrograms] section 02/12/2008 12:49:28.437,d:\xpsp\base\ntsetup\syssetup\syssetup.c,3960,END_SECTION,Processing [RunPrograms] section 02/12/2008 12:49:28.658,d:\xpsp\base\ntsetup\syssetup\syssetup.c,2715,,Power scheme: laptop. 02/12/2008 12:49:28.708,d:\xpsp\base\ntsetup\syssetup\syssetup.c,2719,,SetActivePwrScheme succeeded. 02/12/2008 12:49:34.716,d:\xpsp\base\ntsetup\syssetup\log.c,133,,The external program exportreg.cmd returned exit code 0. 02/12/2008 12:49:34.726,d:\xpsp\base\ntsetup\syssetup\syssetup.c,4018,BEGIN_SECTION,Saving hives 02/12/2008 12:49:34.826,d:\xpsp\base\ntsetup\syssetup\syssetup.c,4032,END_SECTION,Saving hives 'exportreg.cmd' is what I had executing at the cmdlines.txt point in installation and considering how close it is to the Virtual Memory setting stage of installation, it seemed a perfect point to set that as well: REG ADD "HKLM\SYSTEM\CURRENTCONTROLSET\CONTROL\SESSION MANAGER\MEMORY MANAGEMENT" /V PagingFiles /t REG_MULTI_SZ /d "E:\pagefile.sys 1800 1800" /f I think I'll have to settle for setting my environmental variables using cmdlines, its not as neat / perfect as I'd have wanted it but beggars can't be choosers!.