The field type of "Date" automatically includes the Date/Time stamp. I only played with it for a few minutes but I haven't found a way to alter the values in this field via vbscript.
Do you have to utilize a Date field or could you use a Text field instead? If you could utilize a text field, I'd set the default value of the text control to populate the current date and then use some vbscript to only grab the first ten characters from the left.
Via ArcPad Studio:
Go into the properties of the Text control (within the Edit Form) and set it's default value to Now(). This will automatically record the Date/Time within the text field when the edit form is opened.
During the onload event of the form, you could do something similar to the following:
ThisEvent.Object.Pages("page1").Controls("txtDate_Field").Value = Left(ThisEvent.Object.Pages("page1").Controls("txtDate_Field").Value, 10)
What you'll find when you open the edit form is that your Date field (that's a text field type) will have the date written as:
2011-11-09
Just a thought.