datetime handling in VB.Net2005 and SQLserver2000

[Winla]

I am seeking a better way to handle DateTimePicker control as an
optional field for users, a scenario is like this:

• In a user interface I have a datetimepicker control for user to select
  a date as an option.
• In Sql server 2000, I have a datetime field to hold its value or set to null
  if it has no value.
• I have two stored procedures to handle saving into database and
  loading into my program with a datetime parameter as either a string
  or datetime.

The way I am using in previous programs is like this:

• In the database, set a datatime field with null as default value.
• In stored procedure, the parameter for the datetime is set as a
  varchar(10) with default value of '', whenever the datetime is '' in the
  save procedure, it must be set a null value for the datetime field in
  the Database table in INsert or Update syntax.
• In .Net program, the value in DateTimePicker must be converted to
  string when calling the stored procedure, If the datatime is not selected,
  its value is "". When loading the data from database, if datetime is null,
  it must be converted into a string "", then when loading ""
  into Datetimepicker , the control is unchecked to show no date was selected.

Do you have a better way to handle this? like using System.Nullable class
or using datetime datatype as parameter in SPs.

Thanks. Your feedback is appreciated very much.