ObjectARX is both environment and database version specific, meaning that there is a different ARX file for each AutoCAD 2013 32-bit, and AutoCAD 2013 64-bit (two ARX files).
Windows 7 has nothing to do with this... The only correlation to Windows 7 might be if you previously had a 32-bit OS (i.e., Vista, XP, etc.), and are now using Windows 7 64-bit... But again, that's an environment (processing) issue.
In any event, ArxDbg (ObjectARX) and MgdDbg (.NET) are both great tools, and can be downloaded in Autoloader .bundle format from your local ".bundle Thrift Shop" here.