If you’re talking about a disk that doesn’t contain a Windows installation, just use the “TAKEOWN” and “ICACLS” utilities:
TAKEOWN /f "X:\" /r /d y
ICACLS "X:\" /reset /T
Then you can reset the ACLs to whatever you want.
If it’s a disk with a Windows 2000, XP, or Server 2003 operating system installed (don’t know about Vista on this one) you could try re-applying the default security template:
secedit /configure /db secedit.sdb /cfg %SystemRoot%\defltwk.inf /overwrite /verbose
(On a Windows Server install, substitute “defltsv.inf” for “defltwk.inf”.)