Publish Sharepoint 2010 FB via ISA 2006

Hi everybody

I have a intranet site on a specific port.we extended this intranet site in another port for my form base users(It is for my internet users to connect form base not by my AD users).now I have a problem in publishing via ISA 2006.My form base url is like:http://My Public ISA server IP:Port/_layouts/customLogin/SignInform.aspx.but I can not Publish this site with this format.I can Publish the url like:

http://My Public ISA server IP:Port.Please guied me how I can Achive this.

In fact I want to publish a sharepoint Site(Form base) with this url http://My Public ISA server IP:Port/_layouts/customLogin/SignInform.aspx via ISA 2006.AAM also is configured in my Site .How Can I Implement this?

thanks