How to find out if a record already exists in a database, If it doesn't Insert A New Record: http://www.dmxzone.com/ShowDetail.asp?NewsId=4615
Here's a quick example from the link above:
strSQL = "SELECT * FROM MyTable WHERE username = '" & _
Request.Form("username") & "'"
Set rs = db.Execute()
If rs.EOF Then
'Record does not exist
Response.Write "Record exists"