Date handling query in SQL

[BinkyM]

Folks:

I've inherited a SQL database in which a date is kept in a datetime-type field. I have no idea how to do a query on it. My first (and only) thought was to try:

select user_name from AHmembers where signup_date > "2006-02-13 23:59:59"

but that didn't work. I can't find anything in the MySQL 5.0 documentation that tells me how to accomplish what it is I'm looking to do. I'd be way grateful for a pointer!