If you want to run applications or are dealing with large driver sets in WinPE 2.0 it might be useful to increase the scratch space size. Credit goes to Paul Foty...

Here is the registry key and the settings for adjusting the size.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\FBWF]
"WinPECacheThreshold"=dword:00000010

;dword:00000010 = 16
; 0x10 = 16Mb
; 0x18 = 24Mb
; 0x20 = 32Mb
; 0x30 = 48Mb
; 0x40 = 64Mb
; 0x48 = 72Mb
; 0x60 = 96Mb
; 0x80 = 128Mb
; 0x100 = 256Mb