The descriptions for each of the column in the table are stored in a system
table called sysproperties, but it is not documented in SQL Server Books
Online. So accessing this table directly is not generally recommended
however, you can do the following in t-SQL:

SELECT s2.id, s1.name,
( SELECT s3.value
FROM sysproperties s3
WHERE s3.id = s1.id
AND s3.smallid = s1.colid ) AS "col desc"
FROM syscolumns s1
INNER JOIN sysobjects s2
ON s1.id = s2.id
WHERE s2.name = @tbl ;

If you are looking for a documented method, you can use a system function
called fn_listextendedproperty.

SELECT *
FROM ::fn_listextendedproperty (
NULL, 'user', 'dbo', 'table', 'tbl', 'column', DEFAULT ) ;

More details on using extended properties, along with examples, can be found
in SQL Server Books Online.

--
Anith