Optional Where Clause

Hi, I'm having a problem trying to do optional items in where clause. I'd appreciate some help, heres the code.

select DFD.Col1 as 'Col1',CMD.Col2 as 'Col2'
from Control as DFD,MetaData as
CMD,Columns as DC,Tables as DT
where DFD.GroupID in
({0}) and

(CMD.MetaDataId = DFD.PrimaryID --
or CMD.MetaDataId = DFD.ForeignID -- These are the problem 3 lines
or CMD.MetaDataId=DFD.HumanColumn) --

and DFD.Disabled='N' and CMD.Disabled='N' and DC.ColumnsId=CMD.ColumnId
and DC.Disabled='N' and DT.TablesId=DC.TableID and DT.Disabled='N'



-- For the problem rows I need to be able to optionally search if they're = to MetaDataID. Right now this query will return only rows that have metadataid = PrimaryID or Foreign, Human. I need to be able to return all rows with the optional dependancies.