You will have to set up some rule for the two conditions:
For Date only, time will always be 12:00:00
select convert(datetime,convert(varchar(10),getdate(),101) + ' 12:00:00') as [date]
For Time only, date will always be '1/1/1950'
select convert(datetime,'1/1/1950 ' + convert(varchar(8),getdate(),108)) as [time]
Insert example:
For your table:
create table test
(idno integer identity(1,1),
dateonly datetime,
timeonly datetime)
insert into test
select convert(datetime,convert(varchar(10),getdate(),101) + ' 12:00:00'),
convert(datetime,'1/1/1950 ' + convert(varchar(8),getdate(),108))
Hope this helps.