Treat the date as a normal string, except that you have to make sure the date conforms to the particular date-format of the field, eg short date 01/12/2004.
Furthermore, the you have to place the date between hashes, like this "#01/12/2004#'.
Maybe if you give a more detailed description of how you want to use the date, I could be of more assistance, since there are various date functions. (And of course different implementations for different situations).
Probably the most effective way would be to place a date-time picker on the form. Use the string-value of the date time picker for the @date parameter. If it kicks you out just place it between "#"`es (hashes).
(Sorry I don't have my code with me right now, but I reckon it's straightforward enough)