I Know I'm Stupid .. Please Help Me Correct Me.

I have two tables:
1) Table that holds all available ports.
2) Table that holds users for each port.

There may be times where one user is getting more than one port at a time.

I've built up an ASP .NET page that will display each user its port/s in one table.
On another table I want to display all the other available ports which the user doesn't posses and can buy to own.

My problem is where I try to build up the query. I just can't get all the other ports in normal display.



For example, this is what I need:

Ports table:
1/1
1/2
1/3
1/4

Users table:
User A , 1/1
User A , 1/2

ASP page display:

------------
User A Holds:
1/1
1/2
------------

Available:
1/3
1/4
------------


Of course the Available option is derived from the User Holds query, and just getting the opposit not equal ports, but I just can't get it !
I've tried all kinds of Joins and nesting SELECT queries with no luck.

I hate SQL. I want to die.