Woah. I saw unpacking iwd's and stopped there.
DONT edit the iwd's in any way besides exporting the iwi's for editing, then copy/pasting them back in. Use pakscape to open/explore iwd's instead of Winrar. It will save you a lot of trouble.
In pakscape right click on the file you want to edit, and click Object>export to pull a file out for editing, without messing up the IWD. After you get done editing, CRCfix, then paste the file back in using pakscape, overwriting the original.