ARD would require that you have VNC software on the Windows system. But control is all it can do - none of the reporting or management features are supported on Windows - so ARD would be overkill if all you wish to do is connect to a Windows system.
As to CoRD not working, there are many reasons why that might not work, from remote connection not being set up on the Windows system to your company blocking access from outside the network. I'd suggest first that you see if you can access your Windows system from your Mac when it's connected to your company network. If it can't, then either your Windows system or your Mac aren't set up correctly. If it can connect, talk to your company's IT department and ask if they even allow remote access to systems on their network.
Have you considered talking your companies IT team to see if this is some thing they'll support you in doing? If they do, they should be able to tell you if you figure out what kind of client you need: VNC, Window Remote Desktop, LogMeIn, TeamViewer, extra.
If you have the blessing of your company to remote into your work computer; but your company is small enough not to have an IT team. Have you considered LogMeIn?