Question regarding Installation of Firewall on a remote system

Hi, I use Remote Desktop Connection to remotely manage a Windows 2003 Server System.
I had a rather frustrating experience once, when I had accidentally enabled the Windows Firewall, and then was unable to connect using RDP.

I wanna be sure, if I install Comodo Firewall on such a remote system, would I able to remote access it again ?
Is there a certain procedure to allow ports before the firewall is activated ?