Try this:
access-list acl_out deny ip 208.178.50.0 255.255.255.0 any

Or block all Active-X at the firewall..

If you are interested in blocking other spyware besides just Gator, I would suggest setting up an Intrusion Detection Server.  An IDS will sit just outside (or just inside) your firewall, and actively monitor traffic in and out of your network.  Similar to a virus scanner it will look for patterns in the passing data and alert you when suspicious activity is noted.  You will recieve detailed information with specific port numbers, etc.  Armed with this specific information you will be able to easily block the harmful traffic at the firewall.

I should mention that SNORT is a freely available IDS solution that is used by everyone from home hobbyists to large corporations.  You can learn more at http://www.snort.org

This one has worked for me: make a note of the folders Gator use, they're easily found in the registry (Gator changes from time to time some locations). Get rid of all the stuff, then create empty files with the same name of the folders and make them read-only, store the files at the same locations originally used by the folders. Gator will not be able to install again.

There's also a dll in %system% which you might also want to replace with a folder with the same name of the original Gator file.

If you want to block all spyware, you can use spyware detector software such as ad aware. It will help you to get rid of all the sypware found on your system. The downside is some software will not be working properly after the spyware is remove.

I know this has been answered I just want to give my end.. Hope its useful.

This is something I had to do to get rid of Gator Software which works for me. Deny all access to the from the firewall but also try and run this batch in the logon scripts. This works for a number of programs that use the same installer as gator ie Yahoo.

@ECHO OFF
C:
CD\
CD Program Files

REM Detects if Gator Companion software is installed and if so uninstalls it. (Precision Time)

IF EXIST PrecisionTime (
        CD PrecisionTime
    ) ELSE (
        GOTO END:
    )

IF EXIST INSTALL.LOG (
        UNWISE.EXE /S INSTALL.LOG
    ) ELSE (
        GOTO :END
    )
:END

REM Detects if Gator Companion software is installed and if so uninstalls it. (Date Manager)

C:
CD\
CD PROGRAM FILES

IF EXIST "Date Manager" (
        CD "Date Manager"
    ) ELSE (
        GOTO END2:
    )

IF EXIST INSTALL.LOG (
        UNWISE.EXE /S INSTALL.LOG
    ) ELSE (
        GOTO :END2
    )
:END2

What I did to block gator was I went and edited a file called hosts (which is in the system32 folder)with notepad and added a line "127.0.0.1 208.178.50.0" and 208.178.50.0 being the address, I'm able to block everything from this address.