In SQL 2008 and 2005 a simple SQLCLR function that leverages the TryParse method of the Int32 object is the most complete way to check for whether a string value can be cast to a SQL INTEGER. Here is a SQLCLR for you:

[font="Courier New"]using System;

using System.Data;

using System.Data.SqlClient;

using System.Data.SqlTypes;

using Microsoft.SqlServer.Server;

public partial class UserDefinedFunctions

{

    [Microsoft.SqlServer.Server.SqlFunction]

    public static SqlBoolean IsInt32(SqlString Input)

    {

        if (Input.IsNull)

            return SqlBoolean.False;

        else

        {

            Int32 i;

            return Int32.TryParse(Input.Value, out i);

        }

    }

}

[/font]

It is worth noting that in SQL 2012 the TRY_PARSE function was added to T-SQL language making this a trivial chore.