mssql query

I've used mysql a little, but now I'm working with a MS SQL SERVER 2000 database. We have a proprietary application/hardware setup where when a person enters the building, the time they enter the building is automatically put into the database in a field called eventtime, and their access card is entered in a field called cardnum. The time entered is like the mysql NOW() function (i dunno what its called in mssql), the format is YYYY-MM-DD HH:MM:SS.000 anyway. I need to write an SQL query that will get a unique count of cardnum based on how many times the person enters a building each day. So I need to do some sort of UNIQUE (although in mssql I think its distinct) count on the YYYY-MM-DD and ignore the HH:MM:SS.000, but looking at the mssql reference book I have, it doesn't go into great detail on date functions, so I was wondering if anyone knows how to do a unique on the eventtime with the date and ignore the time.