using equal and not equal in a linq join

LINQ only supports equality joins, there's not a way to use a different operator in the join itself.

As you point out, you can just use a where statement for the same effect. If you didn't have an equality comparison to join on, you can use multiple from clauses.

From MSDN:

The equals operator

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A join clause performs an equijoin. In other words, you can only base matches on the equality of two keys. Other types of comparisons such as "greater than" or "not equals" are not supported. To make clear that all joins are equijoins, the join clause uses the equals keyword instead of the == operator. The equals keyword can only be used in a join clause and it differs from the == operator in one important way. With equals, the left key consumes the outer source sequence, and the right key consumes the inner source. The outer source is only in scope on the left side of equals and the inner source sequence is only in scope on the right side.

Non-Equijoins

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You can perform non-equijoins, cross joins, and other custom join operations by using multiple from clauses to introduce new sequences independently into a query. For more information, see How to: Perform Custom Join Operations (C# Programming Guide).

Not equal join could be achieved like,

var result =  from Or in context.orders
          join Usr in context.vw_AllUsers on 
          new { userid = Or.UserId, IsNotAnAdmin = true}
          equals
          new { userid = Usr.UserId, IsNotAnAdmin = (Usr.RoleName != "Admin") }
          select ........

The sql equivalent for the above linq will have a case statement in the join condition.