I read that thread again you linked to on Hard Forum. Joe_Average mentions that RT7 lite makes alterations to files? Can anybody elaborate on that?
"The issue I'm concerned with is that RT Seven Lite makes some alterations to files when it creates a specific edition ISO that won't be exactly the same as the "official" ISO from Microsoft, hence me knowing that this was just an exercise and not a serious thing at this point. I won't use this SP1 integrated installation USB stick (or the ISO I created) for client machines, only my own hardware for the testing until that official ISO appears. "
You have to be in a 64bit environment to slipstream a 64bit iso.
And why is that? If you have a Windows 7 x64 pre SP1 DVD doesn't it just need the files from that and the SP1 package downloaded from MS? Why does it matter what version of Windows you run it on?