try along these lines .....

select * from Tname

where (Tcol1 = @X OR Tcol1 is null)

AND (Tcol2 = @Y OR Tcol2 is null)

---- OR -----

select * from Tname

where Tcol1 = case when @X is null then null

when @X = 0 then null

else @X end

and

Tcol2 = case when @Y is null then null

when @Y = 0 then null

else @Y end