I have installed DNN433 on my own IIS6.0 and it works fine internally. I can access it from any computer in internal network, but not be able to see it from outside. Can anyone help me here?

My current setting as below:
Webserver
1. IIS 6.0 with multiple sites, seperated by Host Header
2. SQL 2000
3. DNN433
4. Win2003 enterprise edition.

ISA server
1. Win2003 enterprise edition.
2. ISA 2004

Additional Info:
1. I have add http://webserver/viscodnn4 into the alias list, so I can access the DNN4 site from any internal client

2. I also added both of dnn4.viscousa.com and dnn4.viscousa.com/viscodnn4 as portal aliase. And published this website in ISA2004. And selected 'Forward the original host header instead of the actual one' option.
When I tired to access the http://dnn4.viscousa.com/viscodnn4 from outside of my company,  error shows up: "The page cannot be displayed"

3. But I can see the picture under DNN4 folder from outside by accessing the URL:http://dnn4.viscousa.com/viscodnn4/403-3.gif
It means the ISA setting should be right.

4. I already gave IUser full control of the viscodnn4 folder.

My question is:
Can I publish a DNN433 website through ISA2004? If yes, how to do it?

No, I have only allow internal SQL access. I don't want outside access to my SQL DB except Webbase program. But the problem is my ISA2004, IIS6.0 and SQL DB are located on one server.
And all the other webiste which need connect to the Local Database are work no problem.