I'm confused, are you wanting to record the date of the registration within the information you're recording about the registration? Or in a separate record/table?
If you simply want the current date/time within the same record it's as simple as adding a date/time column in your table and populating it either from the code-behind side with DateTime.Now or on the SQL side with (I think) dateTime.Now() (been a while since I used the commands directly within SQL).