stored proc with datetime

i need a little syntax help with a SP.
i have a datetime field that is part of the search criteria.
it may be null in which case it should be ingnored or get all dates.
if a date parameter is passed it should find it.

it only works for all when the arrivaldate is a varchar.
	@[EMAIL PROTECTED]
 varechar(10) = '%',

and only finds the matching date when
	@[EMAIL PROTECTED]
 smalldatetime,

?