Like this?
set objSysInfo = CreateObject("ADSystemInfo")
strComputerDN = objSysInfo.ComputerName
"wscript.echo strComputerDN"
intStart=InStr(0,strComputerDN,"ou=PUBLIC")
if intStart <> 0 then
intEnd=InStr(intStart,strComputerDN,",")
strOU = mid(strComputerDN,intStart,intEnd)...