ok load PE system hive under "PE" name and apply reg file with the following contents
Windows Registry Editor Version 5.00
as Sha0 pointed out imagePath may not be necessary. This will look for system32\drivers\httpdisk.sys so ensure it's there in your wim.
once booted in PE you can verify if service started by command "net stop httpdisk" and then by starting "net start httpdisk". If you don't get any errors it should work. I just done this on my test PE and I successfully mapped drive and was able to dir and cd in your w7.iso file. Hope this will do the trick for you. Good luck.
Edited by andriusst, 10 January 2013 - 11:14 PM.