Data Manipulation

Hello,

I have to perform some data manipulation based on ID1, ID2 with respect to Effective dates (below represented as effdt)
Source Code:

create table #source (id1 int, id2 int, effdt datetime)
insert into #source values (111, 123, '1/1/2007')
insert into #source values (111, 123, '3/1/2007')
insert into #source values (111, 123, '4/1/2007')
insert into #source values (111, 124, '5/1/2007')
insert into #source values (111, 125, '6/1/2007')
insert into #source values (111, 123, '7/1/2007')

Source Code Data:

ID1 ID2 Effdt
111 123 1/1/2007
111 123 3/1/2007
111 123 4/1/2007
111 124 5/1/2007
111 125 6/1/2007
111 123 7/1/2007

Target Data should look like:

ID1 ID2 Effdt Expdt
111 123 1/1/2007 4/30/2007
111 124 5/1/2007 5/31/2007
111 125 6/1/2007 6/30/2007
111 123 7/1/2007 7/31/2007


The logic is like the min(effdt) as effdt, min(effdt) - 1 as expdt of the next id2 from the source. Nut the problem comes when the same ID2 comes later after a different id2, so just a group by on id1, id2 does not suffice.
If it is the last record then the expdt is that month's end date.
Can someone throw me some light on what kind of logic I should be using to accomplish this.

Thanks in advance.
Greg