select identity(int,1,1) as rownum,* into #t1 from table1
select identity(int,1,1) as rownum,* into #t2 from table2
update b set b.b=a.b from #t1 a,#t2 b where a.rownum=b.rownum
truncate table table1
insert into table1 select a,b,c from #t2
drop table #t1
drop table #t2