My OS mod was locked almost a month ago, I know why but thats not the issue. I want to ask, which versions of Windows can be used to make a "custom" OS? Can I use a pre-rtm version(like 1-3 builds before RTM), or can it only be an abandoned version of windows?

Not really... I used a RTM version of Windows and that caused the lock.

Anything can be modified. All you need to do is take your tools to your desired target.

uhh. yes anything can be modified with a nice good old fashioned hex editor or even

*GASP*

a magnetized needle and a hard disk!

if you want to modify Windows it's your responsibility to backwards engineer it (! LEGALLY QUESTIONABLE !). Understand it, and make it work like how you want it to work. By writting your own code, and modifying existing code.

and you also should define 'modification' a bit clearer. Because typing in something dumb like

could be considered a modification

Use Windows XP, use Whistler, use Neptune, use Longhorn(if you have sooooo much time...), use Vista, use Windows 7, you have a choice. And because RTM version locked up, then you must did something bad(registry, winlogon, whatever what belongs to activation or something).

It CAN be done to anything. If it breaks, you're doing it wrong.

Your topic, from the looks of it, was locked because you distributed the 7600 ISO as part of the project. Windows 7 is still ages away from abandonware, so I don't think that'd be allowed. Turn it into a customisation project and distribute it as an EXE installer, perhaps?

you can use even RTM versions
as long (as said above) you don't distribute whole ISO
but rather installer that patches things

then burden is not on you, but on those who actually run/use installer