You can use the following:
select t1.col1,
t1.col2,
t1.col3,
left(t2.col4, len(t2.col4)-1) col4
from table1 t1
cross apply
(
select cast(t2.Col4 as varchar(10)) + ', '
from Table2 t2
where t1.col1 = t2.col1
FOR XML PATH('')
) t2 (col4)
See SQL Fiddle with Demo.
Or you can use:
select t1.col1,
t1.col2,
t1.col3,
STUFF(
(SELECT ', ' + cast(t2.Col4 as varchar(10))
FROM Table2 t2
where t1.col1 = t2.col1
FOR XML PATH (''))
, 1, 1, '') AS col4
from table1 t1