You can join on DateDiff(dd, Date1, Date2) < x

Or to get more exact

select endOfMonth.*, begOfMonth.* 
from endOfMonth join begOfMonth 
on DATEADD (dd , 1 , endOfMonth.date ) = begOfMonth.Date

Your ON clause could look at year and quarter for a match:

ON TABLE1.YEAR([1st quarter end ]) = TABLE2.YEAR([1st quarter end ])
AND TABLE1.QUARTER([1st quarter end ]) = TABLE2.QUARTER([1st quarter end ])

One approach would be to use the DATEPART() function that returns the quarter for any given date. Then you would be able to join on the returned quarter.

Sample SQL:

SELECT *
FROM 
(
    SELECT DATEPART(QUARTER,date_column) AS t1_quarter
    FROM table1
    UNION ALL
    SELECT DATEPART(QUARTER,date_column) AS t2_quarter
    FROM table2
) AS temp
WHERE temp.t1_quarter = temp.t2_quarter;

Put any other fields as you require (ID fields most probably) in the internal SELECTS.

If I rigthly understood you and you have the same number of column in those tables then you should use UNION in your SQL-query. See more information about UNION here: http://en.wikipedia.org/wiki/Set_operations_%28SQL%29 .

select 
  val1 
From 
  Table1 T1 
  inner Join Table2 t2 
  on MONTH(T1.date1) = MONTH(t2.date1) 
  And YEAR(T1.date1) = YEAR(t2.date1)